diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a814cc5e8..61cb3ee27 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,7 +12,7 @@ jobs:
     name: "Tests and Analysis (JDK: ${{ matrix.jdk }})"
     strategy:
       matrix:
-        jdk: [ 11, 17, 21 ]
+        jdk: [ 17, 21, 25 ]
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -56,7 +56,7 @@ jobs:
     needs: [ tests-and-analysis ]
     strategy:
       matrix:
-        jdk: [ 11, 17, 21 ]
+        jdk: [ 17, 21, 25 ]
         os: [ ubuntu-latest, windows-latest, macOS-latest ]
     runs-on: ${{ matrix.os }}
     steps:
@@ -99,7 +99,7 @@ jobs:
         uses: actions/setup-java@v3
         with:
           distribution: 'zulu'
-          java-version: 11
+          java-version: 17
       - name: Set up cache
         uses: actions/cache@v3
         with:
@@ -150,7 +150,7 @@ jobs:
         uses: actions/setup-java@v3
         with:
           distribution: 'zulu'
-          java-version: 11
+          java-version: 17
       - name: Set up cache
         uses: actions/cache@v3
         with:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a3d68f22..ef261e8de 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,7 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Changed
 
-* LearnLib now requires Java 11 at runtime.
+* LearnLib now requires Java 17 at runtime.
 * The `generateTestWords` method of `AbstractTestWordEQOracle` now needs to be public.
 
 ### Fixed
diff --git a/README.md b/README.md
index dd2610ed6..b924e69d6 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@ Contributions -- whether it is in the form of new features, better documentation
 
 For simply using LearnLib you may use the Maven artifacts which are available in the [Maven Central repository][maven-central].
 It is also possible to download a bundled [distribution artifact][maven-central-distr] if you want to use LearnLib without Maven support.
-Note that LearnLib requires Java 11 (or newer) to build but still supports Java 8 at runtime.
+Note that LearnLib requires Java 17 (or newer) to build and run.
 
 #### Building development versions
 
diff --git a/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/AbstractAbstractionTree.java b/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/AbstractAbstractionTree.java
index 7402d3afb..c34e4f530 100644
--- a/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/AbstractAbstractionTree.java
+++ b/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/AbstractAbstractionTree.java
@@ -132,8 +132,7 @@ public Collection<CI> getRepresentativeSymbols() {
 
     @Override
     public Collection<Node> getOutgoingEdges(Node node) {
-        if (node instanceof InnerNode) {
-            final InnerNode<?, ?> n = (InnerNode<?, ?>) node;
+        if (node instanceof InnerNode<?, ?> n) {
             return Arrays.asList(n.equalsNext, n.otherNext);
         }
 
@@ -155,8 +154,7 @@ public Collection<Node> getNodes() {
 
         while (!nodes.isEmpty()) {
             final Node n = nodes.poll();
-            if (n instanceof InnerNode) {
-                final InnerNode<?, ?> in = (InnerNode<?, ?>) n;
+            if (n instanceof InnerNode<?, ?> in) {
                 result.add(in);
                 nodes.add(in.equalsNext);
                 nodes.add(in.otherNext);
@@ -177,11 +175,9 @@ public VisualizationHelper<Node, Node> getVisualizationHelper() {
             public boolean getNodeProperties(Node node, Map<String, String> properties) {
                 super.getNodeProperties(node, properties);
 
-                if (node instanceof InnerNode) {
-                    final InnerNode<?, ?> n = (InnerNode<?, ?>) node;
+                if (node instanceof InnerNode<?, ?> n) {
                     properties.put(NodeAttrs.LABEL, n.prefix + ", " + n.suffix);
-                } else if (node instanceof Leaf) {
-                    final Leaf<?, ?> l = (Leaf<?, ?>) node;
+                } else if (node instanceof Leaf<?, ?> l) {
                     properties.put(NodeAttrs.LABEL, String.format("Abs.: '%s'%nRep.: '%s'", l.abs, l.rep));
                 }
 
@@ -192,8 +188,7 @@ public boolean getNodeProperties(Node node, Map<String, String> properties) {
             public boolean getEdgeProperties(Node src, Node edge, Node tgt, Map<String, String> properties) {
                 super.getEdgeProperties(src, edge, tgt, properties);
 
-                if (src instanceof InnerNode) {
-                    final InnerNode<?, ?> n = (InnerNode<?, ?>) src;
+                if (src instanceof InnerNode<?, ?> n) {
                     if (n.equalsNext == tgt) {
                         properties.put(EdgeAttrs.LABEL, "== " + n.out);
                     } else {
diff --git a/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/Node.java b/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/Node.java
index 174a6acc3..6d9700948 100644
--- a/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/Node.java
+++ b/algorithms/active/aaar/src/main/java/de/learnlib/algorithm/aaar/abstraction/Node.java
@@ -17,7 +17,7 @@
 
 import net.automatalib.word.Word;
 
-class Node {
+public class Node {
 
     static class InnerNode<CI, D> extends Node {
 
diff --git a/algorithms/active/aaar/src/test/java/de/learnlib/algorithm/aaar/explicit/ModuloInitialAbstraction.java b/algorithms/active/aaar/src/test/java/de/learnlib/algorithm/aaar/explicit/ModuloInitialAbstraction.java
index 428b9ac46..f1a8fc9ae 100644
--- a/algorithms/active/aaar/src/test/java/de/learnlib/algorithm/aaar/explicit/ModuloInitialAbstraction.java
+++ b/algorithms/active/aaar/src/test/java/de/learnlib/algorithm/aaar/explicit/ModuloInitialAbstraction.java
@@ -40,14 +40,11 @@ public String getAbstractSymbol(CI c) {
 
     @Override
     public CI getRepresentative(String a) {
-        switch (a) {
-            case "even":
-                return alphabet.getSymbol(0);
-            case "odd":
-                return alphabet.getSymbol(1);
-            default:
-                throw new IllegalArgumentException("Unknown symbol: " + a);
-        }
+        return switch (a) {
+            case "even" -> alphabet.getSymbol(0);
+            case "odd" -> alphabet.getSymbol(1);
+            default -> throw new IllegalArgumentException("Unknown symbol: " + a);
+        };
     }
 
     @Override
diff --git a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/ADTExtender.java b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/ADTExtender.java
index 43405be41..7ea725ff4 100644
--- a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/ADTExtender.java
+++ b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/ADTExtender.java
@@ -24,6 +24,7 @@
  * Interface for configuration objects that specify how to finalize the temporary splitter given by regular
  * counterexample decomposition.
  */
+@FunctionalInterface
 public interface ADTExtender {
 
     /**
diff --git a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/LeafSplitter.java b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/LeafSplitter.java
index 14b7464e6..ea2784d96 100644
--- a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/LeafSplitter.java
+++ b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/LeafSplitter.java
@@ -22,6 +22,7 @@
  * Interface for configuration objects that specify how to split the ADT leaf of a hypothesis state that needs
  * refinement.
  */
+@FunctionalInterface
 public interface LeafSplitter {
 
     /**
diff --git a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/SubtreeReplacer.java b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/SubtreeReplacer.java
index 17bbd3ec2..77e58d3e5 100644
--- a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/SubtreeReplacer.java
+++ b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/api/SubtreeReplacer.java
@@ -25,6 +25,7 @@
 /**
  * Interface for configuration objects that specify how nodes of the current ADT should be replaced.
  */
+@FunctionalInterface
 public interface SubtreeReplacer {
 
     /**
diff --git a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/ADSCalculator.java b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/ADSCalculator.java
index f4a446105..f176f3881 100644
--- a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/ADSCalculator.java
+++ b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/ADSCalculator.java
@@ -22,6 +22,7 @@
 import net.automatalib.alphabet.Alphabet;
 import net.automatalib.automaton.transducer.MealyMachine;
 
+@FunctionalInterface
 public interface ADSCalculator {
 
     <S, I, O> Optional<ADTNode<S, I, O>> compute(MealyMachine<S, I, ?, O> hypothesis,
diff --git a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/DefensiveADSCalculator.java b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/DefensiveADSCalculator.java
index c8908fcb4..218704dc9 100644
--- a/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/DefensiveADSCalculator.java
+++ b/algorithms/active/adt/src/main/java/de/learnlib/algorithm/adt/config/model/DefensiveADSCalculator.java
@@ -23,6 +23,7 @@
 import net.automatalib.alphabet.Alphabet;
 import net.automatalib.automaton.transducer.MealyMachine;
 
+@FunctionalInterface
 public interface DefensiveADSCalculator {
 
     <S, I, O> Optional<ADTNode<S, I, O>> compute(MealyMachine<S, I, ?, O> automaton,
diff --git a/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/dfa/KearnsVaziraniDFA.java b/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/dfa/KearnsVaziraniDFA.java
index 7a0cab966..84a0eda75 100644
--- a/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/dfa/KearnsVaziraniDFA.java
+++ b/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/dfa/KearnsVaziraniDFA.java
@@ -186,9 +186,7 @@ private void updateTransitions(List<Long> transList,
 
         final List<Word<I>> transAs = new ArrayList<>(numTrans);
 
-        for (int i = 0; i < numTrans; i++) {
-            long encodedTrans = transList.get(i);
-
+        for (long encodedTrans : transList) {
             int sourceState = (int) (encodedTrans >> Integer.SIZE);
             int transIdx = (int) encodedTrans;
 
diff --git a/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/mealy/KearnsVaziraniMealy.java b/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/mealy/KearnsVaziraniMealy.java
index 6fe1bd63a..c3535c218 100644
--- a/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/mealy/KearnsVaziraniMealy.java
+++ b/algorithms/active/kearns-vazirani/src/main/java/de/learnlib/algorithm/kv/mealy/KearnsVaziraniMealy.java
@@ -198,9 +198,7 @@ private void updateTransitions(List<Long> transList,
 
         final List<Word<I>> transAs = new ArrayList<>(numTrans);
 
-        for (int i = 0; i < numTrans; i++) {
-            long encodedTrans = transList.get(i);
-
+        for (long encodedTrans : transList) {
             int sourceState = (int) (encodedTrans >> Integer.SIZE);
             int transIdx = (int) encodedTrans;
 
diff --git a/algorithms/active/lambda/src/main/java/de/learnlib/algorithm/lambda/ttt/dt/DTLeaf.java b/algorithms/active/lambda/src/main/java/de/learnlib/algorithm/lambda/ttt/dt/DTLeaf.java
index 09c3d26ca..6b5df86bc 100644
--- a/algorithms/active/lambda/src/main/java/de/learnlib/algorithm/lambda/ttt/dt/DTLeaf.java
+++ b/algorithms/active/lambda/src/main/java/de/learnlib/algorithm/lambda/ttt/dt/DTLeaf.java
@@ -111,8 +111,8 @@ public void split(PTNode<I, D> u1, PTNode<I, D> u2, I a) {
         DTLeaf<I, D> ua2 = s2.state();
         AbstractDTNode<I, D> n = lca(ua1, ua2);
         STNode<I> av;
-        if (n instanceof DTInnerNode) {
-            av = ((DTInnerNode<I, D>) n).suffix().prepend(a);
+        if (n instanceof DTInnerNode<I, D> in) {
+            av = in.suffix().prepend(a);
         } else {
             av = tree.newSuffix(a);
         }
diff --git a/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/LSOracle.java b/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/LSOracle.java
index 980799fb8..9e80c9bcc 100644
--- a/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/LSOracle.java
+++ b/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/LSOracle.java
@@ -78,8 +78,9 @@ private <T> List<T> sample2(Collection<T> collection) {
         return shuffled.subList(0, 2);
     }
 
+    @SuppressWarnings("PMD.SwitchDensity")
     private Pair<Word<I>, Word<O>> rule3IO(List<Word<I>> candidates, Word<I> prefix) {
-        switch (this.rule3) {
+        return switch (this.rule3) {
             case ADS:
                 if (candidates.size() == 2) {
                     Word<I> q1Acc = candidates.get(0);
@@ -92,28 +93,25 @@ private Pair<Word<I>, Word<O>> rule3IO(List<Word<I>> candidates, Word<I> prefix)
                     Word<I> wit = ApartnessUtil.computeWitness(obsTree, q1, q2);
                     assert wit != null;
 
-                    WordBuilder<I> inputSeq = new WordBuilder<>(prefix);
                     assert !(ApartnessUtil.accStatesAreApart(obsTree, prefix, q1Acc) ||
                              ApartnessUtil.accStatesAreApart(obsTree, prefix, q2Acc));
-                    inputSeq.append(wit);
-                    Word<O> outputSeq = this.outputQuery(inputSeq.toWord());
 
-                    return Pair.of(inputSeq.toWord(), outputSeq);
+                    Word<I> inputSeq = prefix.concat(wit);
+                    Word<O> outputSeq = this.outputQuery(inputSeq);
 
+                    yield Pair.of(inputSeq, outputSeq);
                 } else {
                     List<Integer> candss = getSuccs(candidates);
                     ADSTree<Integer, I, O> suffix = new ADSTree<>(obsTree, candss, sinkOutput);
-                    return this.adaptiveOutputQuery(prefix, null, suffix);
+                    yield this.adaptiveOutputQuery(prefix, null, suffix);
                 }
             case SEPSEQ:
                 List<Integer> withS = getSuccs(sample2(candidates));
                 Word<I> wit = ApartnessUtil.computeWitness(obsTree, withS.get(0), withS.get(1));
                 assert wit != null;
                 Word<I> inputSeq = prefix.concat(wit);
-                return Pair.of(inputSeq, this.outputQuery(inputSeq));
-            default:
-                throw new IllegalStateException("Shouldn't get here!");
-        }
+                yield Pair.of(inputSeq, this.outputQuery(inputSeq));
+        };
     }
 
     private List<Integer> getSuccs(Collection<Word<I>> candidates) {
@@ -148,14 +146,14 @@ public List<Word<I>> identifyFrontier(Word<I> fsAcc, List<Word<I>> candidates) {
     }
 
     private Pair<Word<I>, Word<O>> rule2IO(Word<I> accessQ, I i, List<Integer> bss, Collection<Word<I>> basis) {
-        switch (this.rule2) {
+        return switch (this.rule2) {
             case ADS:
                 ADSTree<Integer, I, O> suffix = new ADSTree<>(obsTree, bss, sinkOutput);
-                return this.adaptiveOutputQuery(accessQ, i, suffix);
+                yield this.adaptiveOutputQuery(accessQ, i, suffix);
             case NOTHING:
                 Word<I> prefix = accessQ.append(i);
                 Word<O> oSeq = this.outputQuery(prefix);
-                return Pair.of(prefix, oSeq);
+                yield Pair.of(prefix, oSeq);
             case SEPSEQ:
                 Word<I> wit;
                 if (basis.size() >= 2) {
@@ -167,10 +165,8 @@ private Pair<Word<I>, Word<O>> rule2IO(Word<I> accessQ, I i, List<Integer> bss,
                 }
                 Word<I> inputSeq = accessQ.append(i).concat(wit);
                 Word<O> outputSeq = this.outputQuery(inputSeq);
-                return Pair.of(inputSeq, outputSeq);
-            default:
-                throw new IllegalStateException("Shouldn't get here!");
-        }
+                yield Pair.of(inputSeq, outputSeq);
+        };
     }
 
     public List<Pair<Word<I>, List<Word<I>>>> exploreFrontier(Collection<Word<I>> basis) {
diff --git a/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/ads/ADSTree.java b/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/ads/ADSTree.java
index a59ceb48a..72ba6f8a4 100644
--- a/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/ads/ADSTree.java
+++ b/algorithms/active/lsharp/src/main/java/de/learnlib/algorithm/lsharp/ads/ADSTree.java
@@ -110,7 +110,7 @@ public static <S extends Comparable<S>, I, O> ADSNode<I, O> constructADS(Observa
             }
         }
 
-        assert bestInput != null && bestChildren != null;
+        assert bestInput != null;
 
         return new ADSNode<>(bestInput, toMap(bestChildren), bestIScore);
     }
diff --git a/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/AbstractAutomatonLStar.java b/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/AbstractAutomatonLStar.java
index c12b8bc1e..0bf1c8ac5 100644
--- a/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/AbstractAutomatonLStar.java
+++ b/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/AbstractAutomatonLStar.java
@@ -205,7 +205,7 @@ public void resume(AutomatonLStarState<I, D, AI, S> state) {
         }
     }
 
-    static final class StateInfo<S, I> {
+    protected static final class StateInfo<S, I> {
 
         private final Row<I> row;
         private final S state;
diff --git a/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/closing/ClosingStrategy.java b/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/closing/ClosingStrategy.java
index 469773395..5c284e45d 100644
--- a/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/closing/ClosingStrategy.java
+++ b/algorithms/active/lstar/src/main/java/de/learnlib/algorithm/lstar/closing/ClosingStrategy.java
@@ -29,6 +29,7 @@
  * @param <D>
  *         type variable for output symbol upper bound.
  */
+@FunctionalInterface
 public interface ClosingStrategy<I, D> {
 
     /**
diff --git a/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/Splitter.java b/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/Splitter.java
index 750834e94..91393a91d 100644
--- a/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/Splitter.java
+++ b/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/Splitter.java
@@ -65,21 +65,16 @@ public ContextPair<I> getNewDiscriminator() {
         Word<I> prefix = succSeparator.getDiscriminator().getPrefix();
         Word<I> suffix = succSeparator.getDiscriminator().getSuffix();
 
-        switch (type) {
-            case INTERNAL:
-                return new ContextPair<>(prefix, suffix.prepend(symbol));
-            case RETURN:
-                return new ContextPair<>(prefix.concat(location.getAccessSequence()).append(otherSymbol),
-                                         suffix.prepend(symbol));
-            case CALL:
-                return new ContextPair<>(prefix,
-                                         location.getAccessSequence()
-                                                 .prepend(symbol)
-                                                 .append(otherSymbol)
-                                                 .concat(suffix));
-            default:
-                throw new IllegalStateException("Unhandled type " + type);
-        }
+        return switch (type) {
+            case INTERNAL -> new ContextPair<>(prefix, suffix.prepend(symbol));
+            case RETURN -> new ContextPair<>(prefix.concat(location.getAccessSequence()).append(otherSymbol),
+                                             suffix.prepend(symbol));
+            case CALL -> new ContextPair<>(prefix,
+                                           location.getAccessSequence()
+                                                   .prepend(symbol)
+                                                   .append(otherSymbol)
+                                                   .concat(suffix));
+        };
     }
 
     public int getNewDiscriminatorLength() {
diff --git a/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/TTTLearnerVPA.java b/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/TTTLearnerVPA.java
index b7a3ffd86..0aa7fd8db 100644
--- a/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/TTTLearnerVPA.java
+++ b/algorithms/active/ttt-vpa/src/main/java/de/learnlib/algorithm/ttt/vpa/TTTLearnerVPA.java
@@ -218,7 +218,7 @@ protected State<HypLoc<I>> getAnySuccessor(State<HypLoc<I>> state, I sym) {
         final VPAlphabet.SymbolType type = alphabet.getSymbolType(sym);
         final StackContents stackContents = state.getStackContents();
 
-        switch (type) {
+        return switch (type) {
             case INTERNAL: {
                 AbstractHypTrans<I> trans = hypothesis.getInternalTransition(state.getLocation(), sym);
                 HypLoc<I> succLoc;
@@ -227,11 +227,11 @@ protected State<HypLoc<I>> getAnySuccessor(State<HypLoc<I>> state, I sym) {
                 } else {
                     succLoc = trans.getNonTreeTarget().subtreeLocsIterator().next();
                 }
-                return new State<>(succLoc, stackContents);
+                yield new State<>(succLoc, stackContents);
             }
             case CALL: {
                 int stackSym = hypothesis.encodeStackSym(state.getLocation(), sym);
-                return new State<>(hypothesis.getInitialLocation(), StackContents.push(stackSym, stackContents));
+                yield new State<>(hypothesis.getInitialLocation(), StackContents.push(stackSym, stackContents));
             }
             case RETURN: {
                 assert stackContents != null;
@@ -243,11 +243,9 @@ protected State<HypLoc<I>> getAnySuccessor(State<HypLoc<I>> state, I sym) {
                 } else {
                     succLoc = trans.getNonTreeTarget().subtreeLocsIterator().next();
                 }
-                return new State<>(succLoc, stackContents.pop());
+                yield new State<>(succLoc, stackContents.pop());
             }
-            default:
-                throw new IllegalStateException("Unhandled type " + type);
-        }
+        };
     }
 
     private PrefixTransformAcex deriveAcex(OutputInconsistency<I> outIncons) {
@@ -592,16 +590,11 @@ private static <I> void markAndPropagate(DTNode<I> node, Boolean label) {
     }
 
     public AbstractHypTrans<I> getSplitterTrans(HypLoc<I> loc, Splitter<I> splitter) {
-        switch (splitter.type) {
-            case INTERNAL:
-                return hypothesis.getInternalTransition(loc, splitter.symbol);
-            case RETURN:
-                return hypothesis.getReturnTransition(loc, splitter.symbol, splitter.location, splitter.otherSymbol);
-            case CALL:
-                return hypothesis.getReturnTransition(splitter.location, splitter.otherSymbol, loc, splitter.symbol);
-            default:
-                throw new IllegalStateException("Unhandled type " + splitter.type);
-        }
+        return switch (splitter.type) {
+            case INTERNAL -> hypothesis.getInternalTransition(loc, splitter.symbol);
+            case RETURN -> hypothesis.getReturnTransition(loc, splitter.symbol, splitter.location, splitter.otherSymbol);
+            case CALL -> hypothesis.getReturnTransition(splitter.location, splitter.otherSymbol, loc, splitter.symbol);
+        };
     }
 
     private static <I> void moveIncoming(DTNode<I> newNode, DTNode<I> oldNode, Boolean label) {
diff --git a/api/src/main/java/de/learnlib/AccessSequenceProvider.java b/api/src/main/java/de/learnlib/AccessSequenceProvider.java
index db3106a62..d0e628522 100644
--- a/api/src/main/java/de/learnlib/AccessSequenceProvider.java
+++ b/api/src/main/java/de/learnlib/AccessSequenceProvider.java
@@ -24,6 +24,7 @@
  * @param <I>
  *         input symbol type
  */
+@FunctionalInterface
 public interface AccessSequenceProvider<I> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/AccessSequenceTransformer.java b/api/src/main/java/de/learnlib/AccessSequenceTransformer.java
index 20e995117..3e33439ae 100644
--- a/api/src/main/java/de/learnlib/AccessSequenceTransformer.java
+++ b/api/src/main/java/de/learnlib/AccessSequenceTransformer.java
@@ -17,6 +17,7 @@
 
 import net.automatalib.word.Word;
 
+@FunctionalInterface
 public interface AccessSequenceTransformer<I> {
 
     Word<I> transformAccessSequence(Word<I> word);
diff --git a/api/src/main/java/de/learnlib/TestWordGenerator.java b/api/src/main/java/de/learnlib/TestWordGenerator.java
index 2e8808edb..9fd7f378a 100644
--- a/api/src/main/java/de/learnlib/TestWordGenerator.java
+++ b/api/src/main/java/de/learnlib/TestWordGenerator.java
@@ -29,6 +29,7 @@
  * @param <I>
  *         input symbol type
  */
+@FunctionalInterface
 public interface TestWordGenerator<A, I> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/algorithm/LearnerConstructor.java b/api/src/main/java/de/learnlib/algorithm/LearnerConstructor.java
index b5877fc38..00360baf4 100644
--- a/api/src/main/java/de/learnlib/algorithm/LearnerConstructor.java
+++ b/api/src/main/java/de/learnlib/algorithm/LearnerConstructor.java
@@ -29,6 +29,7 @@
  * @param <D>
  *         output domain type
  */
+@FunctionalInterface
 public interface LearnerConstructor<L, I, D> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/oracle/AdaptiveMembershipOracle.java b/api/src/main/java/de/learnlib/oracle/AdaptiveMembershipOracle.java
index 110ceafad..c554fc60a 100644
--- a/api/src/main/java/de/learnlib/oracle/AdaptiveMembershipOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/AdaptiveMembershipOracle.java
@@ -30,6 +30,7 @@
  * @param <O>
  *         output symbol type
  */
+@FunctionalInterface
 public interface AdaptiveMembershipOracle<I, O> extends BatchProcessor<AdaptiveQuery<I, O>> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/oracle/BatchProcessor.java b/api/src/main/java/de/learnlib/oracle/BatchProcessor.java
index 95ec589d5..0f61f16b8 100644
--- a/api/src/main/java/de/learnlib/oracle/BatchProcessor.java
+++ b/api/src/main/java/de/learnlib/oracle/BatchProcessor.java
@@ -26,6 +26,7 @@
  * @param <T>
  *         batch type
  */
+@FunctionalInterface
 public interface BatchProcessor<T> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/oracle/EmptinessOracle.java b/api/src/main/java/de/learnlib/oracle/EmptinessOracle.java
index 77b55911d..4c629e3ad 100644
--- a/api/src/main/java/de/learnlib/oracle/EmptinessOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/EmptinessOracle.java
@@ -38,6 +38,7 @@
  * @param <D>
  *         the output type
  */
+@FunctionalInterface
 public interface EmptinessOracle<A extends Output<I, D>, I, D> {
 
     default boolean isCounterExample(Output<I, D> hypothesis, Iterable<? extends I> input, D output) {
@@ -46,7 +47,9 @@ default boolean isCounterExample(Output<I, D> hypothesis, Iterable<? extends I>
 
     @Nullable DefaultQuery<I, D> findCounterExample(A hypothesis, Collection<? extends I> inputs);
 
+    @FunctionalInterface
     interface DFAEmptinessOracle<I> extends EmptinessOracle<DFA<?, I>, I, Boolean> {}
 
+    @FunctionalInterface
     interface MealyEmptinessOracle<I, O> extends EmptinessOracle<MealyMachine<?, I, ?, O>, I, Word<O>> {}
 }
diff --git a/api/src/main/java/de/learnlib/oracle/EquivalenceOracle.java b/api/src/main/java/de/learnlib/oracle/EquivalenceOracle.java
index 065c2c747..ee8b75e88 100644
--- a/api/src/main/java/de/learnlib/oracle/EquivalenceOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/EquivalenceOracle.java
@@ -42,6 +42,7 @@
  * @param <D>
  *         output domain type
  */
+@FunctionalInterface
 public interface EquivalenceOracle<A, I, D> {
 
     /**
@@ -66,6 +67,7 @@ public interface EquivalenceOracle<A, I, D> {
      * @param <I>
      *         input symbol class
      */
+    @FunctionalInterface
     interface DFAEquivalenceOracle<I> extends EquivalenceOracle<DFA<?, I>, I, Boolean> {}
 
     /**
@@ -76,6 +78,7 @@ interface DFAEquivalenceOracle<I> extends EquivalenceOracle<DFA<?, I>, I, Boolea
      * @param <O>
      *         output symbol class
      */
+    @FunctionalInterface
     interface MealyEquivalenceOracle<I, O> extends EquivalenceOracle<MealyMachine<?, I, ?, O>, I, Word<O>> {}
 
     /**
@@ -86,6 +89,7 @@ interface MealyEquivalenceOracle<I, O> extends EquivalenceOracle<MealyMachine<?,
      * @param <O>
      *         output symbol class
      */
+    @FunctionalInterface
     interface MooreEquivalenceOracle<I, O> extends EquivalenceOracle<MooreMachine<?, I, ?, O>, I, Word<O>> {}
 
 }
diff --git a/api/src/main/java/de/learnlib/oracle/InclusionOracle.java b/api/src/main/java/de/learnlib/oracle/InclusionOracle.java
index 94b8a3f2e..e29ffbf33 100644
--- a/api/src/main/java/de/learnlib/oracle/InclusionOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/InclusionOracle.java
@@ -38,14 +38,17 @@
  * @param <D>
  *         the output type
  */
+@FunctionalInterface
 public interface InclusionOracle<A extends Output<I, D>, I, D> extends EquivalenceOracle<A, I, D> {
 
     default boolean isCounterExample(Output<I, D> hypothesis, Iterable<? extends I> input, D output) {
         return !Objects.equals(hypothesis.computeOutput(input), output);
     }
 
+    @FunctionalInterface
     interface DFAInclusionOracle<I> extends InclusionOracle<DFA<?, I>, I, Boolean>, DFAEquivalenceOracle<I> {}
 
+    @FunctionalInterface
     interface MealyInclusionOracle<I, O>
             extends InclusionOracle<MealyMachine<?, I, ?, O>, I, Word<O>>, MealyEquivalenceOracle<I, O> {}
 }
diff --git a/api/src/main/java/de/learnlib/oracle/LassoEmptinessOracle.java b/api/src/main/java/de/learnlib/oracle/LassoEmptinessOracle.java
index 29caa731a..6ea73d84e 100644
--- a/api/src/main/java/de/learnlib/oracle/LassoEmptinessOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/LassoEmptinessOracle.java
@@ -29,9 +29,12 @@
  * @param <I> the input type
  * @param <D> the output type
  */
+@FunctionalInterface
 public interface LassoEmptinessOracle<L extends Lasso<I, D>, I, D> extends EmptinessOracle<L, I, D> {
 
+    @FunctionalInterface
     interface DFALassoEmptinessOracle<I> extends LassoEmptinessOracle<DFALasso<I>, I, Boolean> {}
 
+    @FunctionalInterface
     interface MealyLassoEmptinessOracle<I, O> extends LassoEmptinessOracle<MealyLasso<I, O>, I, Word<O>> {}
 }
diff --git a/api/src/main/java/de/learnlib/oracle/MembershipOracle.java b/api/src/main/java/de/learnlib/oracle/MembershipOracle.java
index 618a94d48..af716faa6 100644
--- a/api/src/main/java/de/learnlib/oracle/MembershipOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/MembershipOracle.java
@@ -33,6 +33,7 @@
  *
  * @see DefaultQuery
  */
+@FunctionalInterface
 public interface MembershipOracle<I, D> extends QueryAnswerer<I, D>, BatchProcessor<Query<I, D>> {
 
     @Override
@@ -92,6 +93,7 @@ default void processBatch(Collection<? extends Query<I, D>> batch) {
      * @param <I>
      *         input symbol type
      */
+    @FunctionalInterface
     interface DFAMembershipOracle<I> extends MembershipOracle<I, Boolean> {}
 
     /**
@@ -105,6 +107,7 @@ interface DFAMembershipOracle<I> extends MembershipOracle<I, Boolean> {}
      * @param <O>
      *         output symbol type
      */
+    @FunctionalInterface
     interface MealyMembershipOracle<I, O> extends MembershipOracle<I, Word<O>> {}
 
     /**
@@ -118,6 +121,7 @@ interface MealyMembershipOracle<I, O> extends MembershipOracle<I, Word<O>> {}
      * @param <O>
      *         output symbol type
      */
+    @FunctionalInterface
     interface MooreMembershipOracle<I, O> extends MembershipOracle<I, Word<O>> {}
 
 }
diff --git a/api/src/main/java/de/learnlib/oracle/QueryAnswerer.java b/api/src/main/java/de/learnlib/oracle/QueryAnswerer.java
index 7253d326e..0eca103cc 100644
--- a/api/src/main/java/de/learnlib/oracle/QueryAnswerer.java
+++ b/api/src/main/java/de/learnlib/oracle/QueryAnswerer.java
@@ -25,6 +25,7 @@
  * @param <D>
  *         output domain type
  */
+@FunctionalInterface
 public interface QueryAnswerer<I, D> {
 
     default D answerQuery(Word<I> input) {
diff --git a/api/src/main/java/de/learnlib/oracle/SingleAdaptiveMembershipOracle.java b/api/src/main/java/de/learnlib/oracle/SingleAdaptiveMembershipOracle.java
index 975562604..bf0e63da7 100644
--- a/api/src/main/java/de/learnlib/oracle/SingleAdaptiveMembershipOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/SingleAdaptiveMembershipOracle.java
@@ -25,6 +25,7 @@
  * @see AdaptiveMembershipOracle
  * @see SingleQueryOracle
  */
+@FunctionalInterface
 public interface SingleAdaptiveMembershipOracle<I, O> extends AdaptiveMembershipOracle<I, O> {
 
     @Override
diff --git a/api/src/main/java/de/learnlib/oracle/SingleQueryOracle.java b/api/src/main/java/de/learnlib/oracle/SingleQueryOracle.java
index 91b1705ec..ba940dccb 100644
--- a/api/src/main/java/de/learnlib/oracle/SingleQueryOracle.java
+++ b/api/src/main/java/de/learnlib/oracle/SingleQueryOracle.java
@@ -32,6 +32,7 @@
  * @param <D>
  *         output domain type
  */
+@FunctionalInterface
 public interface SingleQueryOracle<I, D> extends MembershipOracle<I, D> {
 
     @Override
@@ -48,10 +49,13 @@ default void processQueries(Collection<? extends Query<I, D>> queries) {
     @Override
     D answerQuery(Word<I> prefix, Word<I> suffix);
 
+    @FunctionalInterface
     interface SingleQueryOracleDFA<I> extends SingleQueryOracle<I, Boolean>, DFAMembershipOracle<I> {}
 
+    @FunctionalInterface
     interface SingleQueryOracleMealy<I, O> extends SingleQueryOracle<I, Word<O>>, MealyMembershipOracle<I, O> {}
 
+    @FunctionalInterface
     interface SingleQueryOracleMoore<I, O> extends SingleQueryOracle<I, Word<O>>, MooreMembershipOracle<I, O> {}
 
 }
diff --git a/api/src/main/java/de/learnlib/query/OmegaQuery.java b/api/src/main/java/de/learnlib/query/OmegaQuery.java
index 183a517c2..9855e7ca8 100644
--- a/api/src/main/java/de/learnlib/query/OmegaQuery.java
+++ b/api/src/main/java/de/learnlib/query/OmegaQuery.java
@@ -102,16 +102,9 @@ public String toString() {
 
     @Override
     public final boolean equals(@Nullable Object o) {
-        if (this == o) {
-            return true;
-        }
-        if (!(o instanceof OmegaQuery)) {
-            return false;
-        }
-
-        final OmegaQuery<?, ?> that = (OmegaQuery<?, ?>) o;
-        return periodicity == that.periodicity && Objects.equals(prefix, that.prefix) &&
-               Objects.equals(loop, that.loop) && Objects.equals(output, that.output);
+        return this == o || o instanceof OmegaQuery<?, ?> that && periodicity == that.periodicity &&
+                            Objects.equals(prefix, that.prefix) && Objects.equals(loop, that.loop) &&
+                            Objects.equals(output, that.output);
     }
 
     @Override
diff --git a/api/src/main/java/de/learnlib/query/Query.java b/api/src/main/java/de/learnlib/query/Query.java
index 458b423bc..0eab8d69c 100644
--- a/api/src/main/java/de/learnlib/query/Query.java
+++ b/api/src/main/java/de/learnlib/query/Query.java
@@ -118,15 +118,8 @@ public final int hashCode() {
 
     @Override
     public final boolean equals(@Nullable Object o) {
-        if (this == o) {
-            return true;
-        }
-        if (!(o instanceof Query)) {
-            return false;
-        }
-
-        final Query<?, ?> that = (Query<?, ?>) o;
-        return Objects.equals(getPrefix(), that.getPrefix()) && Objects.equals(getSuffix(), that.getSuffix());
+        return this == o || o instanceof Query<?, ?> that && Objects.equals(getPrefix(), that.getPrefix()) &&
+                            Objects.equals(getSuffix(), that.getSuffix());
     }
 
     /**
diff --git a/api/src/main/java/de/learnlib/statistic/StatisticCollector.java b/api/src/main/java/de/learnlib/statistic/StatisticCollector.java
index 60d46d740..9919b876a 100644
--- a/api/src/main/java/de/learnlib/statistic/StatisticCollector.java
+++ b/api/src/main/java/de/learnlib/statistic/StatisticCollector.java
@@ -19,6 +19,7 @@
  * A utility interface to indicate that the implementing class collects statistical information that may be obtained via
  * its {@link #getStatisticalData()} method.
  */
+@FunctionalInterface
 public interface StatisticCollector {
 
     /**
diff --git a/api/src/main/java/de/learnlib/sul/ContextExecutableInput.java b/api/src/main/java/de/learnlib/sul/ContextExecutableInput.java
index b4beec05a..b601f9cb8 100644
--- a/api/src/main/java/de/learnlib/sul/ContextExecutableInput.java
+++ b/api/src/main/java/de/learnlib/sul/ContextExecutableInput.java
@@ -26,6 +26,7 @@
  * @param <C>
  *         context
  */
+@FunctionalInterface
 public interface ContextExecutableInput<O, C> {
 
     /**
diff --git a/api/src/main/java/de/learnlib/sul/ExecutableInput.java b/api/src/main/java/de/learnlib/sul/ExecutableInput.java
index eda3e80fe..5bb1ef647 100644
--- a/api/src/main/java/de/learnlib/sul/ExecutableInput.java
+++ b/api/src/main/java/de/learnlib/sul/ExecutableInput.java
@@ -23,6 +23,7 @@
  * @param <O>
  *         output
  */
+@FunctionalInterface
 public interface ExecutableInput<O> {
 
     /**
diff --git a/build-config/src/main/resources/learnlib-pmd-ruleset.xml b/build-config/src/main/resources/learnlib-pmd-ruleset.xml
index 1dae2428e..00802f952 100644
--- a/build-config/src/main/resources/learnlib-pmd-ruleset.xml
+++ b/build-config/src/main/resources/learnlib-pmd-ruleset.xml
@@ -25,7 +25,6 @@ limitations under the License.
     <!-- EXCLUSIONS -->
 
     <rule ref="category/java/bestpractices.xml">
-        <exclude name="AccessorMethodGeneration"/> <!-- irrelevant once we target Java 11 -->
         <exclude name="ArrayIsStoredDirectly"/>
         <exclude name="LooseCoupling"/> <!-- may be enabled once calls on sub-type methods are filtered again -->
         <exclude name="GuardLogStatement"/>
@@ -55,7 +54,6 @@ limitations under the License.
         <exclude name="ShortClassName"/>
         <exclude name="ShortMethodName"/>
         <exclude name="ShortVariable"/>
-        <exclude name="UnnecessaryImport"/> <!-- flags imports required by JavaDoc -->
     </rule>
 
     <rule ref="category/java/design.xml">
@@ -102,22 +100,28 @@ limitations under the License.
 
     <!-- CONFIGS -->
 
+    <rule ref="category/java/codestyle.xml/ConfusingTernary">
+        <properties>
+            <property name="ignoreElseIf" value="true" />
+        </properties>
+    </rule>
+
     <rule ref="category/java/codestyle.xml/EmptyControlStatement">
         <properties>
             <property name="allowCommentedBlocks" value="true" />
         </properties>
     </rule>
 
-    <rule ref="category/java/codestyle.xml/UnnecessaryFullyQualifiedName">
+    <rule ref="category/java/codestyle.xml/TypeParameterNamingConventions">
         <properties>
-            <property name="reportStaticMethods" value="false" />
-            <property name="reportStaticFields" value="false" />
+            <property name="typeParameterNamePattern" value="[A-Z0-9]*" />
         </properties>
     </rule>
 
-    <rule ref="category/java/codestyle.xml/ConfusingTernary">
+    <rule ref="category/java/codestyle.xml/UnnecessaryFullyQualifiedName">
         <properties>
-            <property name="ignoreElseIf" value="true" />
+            <property name="reportStaticMethods" value="false" />
+            <property name="reportStaticFields" value="false" />
         </properties>
     </rule>
 
diff --git a/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzer.java b/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzer.java
index 60647eb59..c2b4920bb 100644
--- a/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzer.java
+++ b/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzer.java
@@ -15,6 +15,7 @@
  */
 package de.learnlib.acex;
 
+@FunctionalInterface
 public interface AcexAnalyzer {
 
     /**
diff --git a/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzers.java b/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzers.java
index d8872950b..27efe5bcb 100644
--- a/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzers.java
+++ b/commons/counterexamples/src/main/java/de/learnlib/acex/AcexAnalyzers.java
@@ -109,14 +109,10 @@ private static Map<String, AbstractNamedAcexAnalyzer> createMap(Map<String, Abst
     }
 
     public static Collection<AbstractNamedAcexAnalyzer> getAnalyzers(Direction dir) {
-        switch (dir) {
-            case FORWARD:
-                return getForwardAnalyzers();
-            case BACKWARD:
-                return getBackwardAnalyzers();
-            default:
-                throw new IllegalArgumentException();
-        }
+        return switch (dir) {
+            case FORWARD -> getForwardAnalyzers();
+            case BACKWARD -> getBackwardAnalyzers();
+        };
     }
 
     public static Collection<AbstractNamedAcexAnalyzer> getForwardAnalyzers() {
diff --git a/commons/counterexamples/src/main/java/de/learnlib/counterexample/GlobalSuffixFinder.java b/commons/counterexamples/src/main/java/de/learnlib/counterexample/GlobalSuffixFinder.java
index 2b1696de4..a454f07f0 100644
--- a/commons/counterexamples/src/main/java/de/learnlib/counterexample/GlobalSuffixFinder.java
+++ b/commons/counterexamples/src/main/java/de/learnlib/counterexample/GlobalSuffixFinder.java
@@ -41,6 +41,7 @@
  * @param <D>
  *         output domain type upper bound
  */
+@FunctionalInterface
 public interface GlobalSuffixFinder<I, D> {
 
     /**
diff --git a/commons/counterexamples/src/main/java/de/learnlib/counterexample/LocalSuffixFinder.java b/commons/counterexamples/src/main/java/de/learnlib/counterexample/LocalSuffixFinder.java
index 051c429c7..8797e24ca 100644
--- a/commons/counterexamples/src/main/java/de/learnlib/counterexample/LocalSuffixFinder.java
+++ b/commons/counterexamples/src/main/java/de/learnlib/counterexample/LocalSuffixFinder.java
@@ -47,6 +47,7 @@
  * @param <D>
  *         output domain type upper bound
  */
+@FunctionalInterface
 public interface LocalSuffixFinder<I, D> {
 
     /**
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/discriminationtree/model/BooleanMap.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/discriminationtree/model/BooleanMap.java
index 4125f908d..a9ff6e79f 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/discriminationtree/model/BooleanMap.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/discriminationtree/model/BooleanMap.java
@@ -203,15 +203,7 @@ public int hashCode() {
 
         @Override
         public boolean equals(@Nullable Object o) {
-            if (this == o) {
-                return true;
-            }
-            if (!(o instanceof BooleanMap.Entry)) {
-                return false;
-            }
-
-            final BooleanMap<?>.Entry that = (BooleanMap<?>.Entry) o;
-            return Objects.equals(key, that.key);
+            return this == o || o instanceof BooleanMap<?>.Entry that && Objects.equals(key, that.key);
         }
     }
 }
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/ObservationTableFeature.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/ObservationTableFeature.java
index 3c7c350aa..a5ef9b232 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/ObservationTableFeature.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/ObservationTableFeature.java
@@ -15,6 +15,7 @@
  */
 package de.learnlib.datastructure.observationtable;
 
+@FunctionalInterface
 public interface ObservationTableFeature<I, D> {
 
     ObservationTable<I, D> getObservationTable();
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/reader/ObservationTableReader.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/reader/ObservationTableReader.java
index 1004a7d2c..b60143ddb 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/reader/ObservationTableReader.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/reader/ObservationTableReader.java
@@ -26,6 +26,7 @@
  * @param <D>
  *         observation (output) domain class
  */
+@FunctionalInterface
 public interface ObservationTableReader<I, D> {
 
     /**
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/writer/ObservationTableWriter.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/writer/ObservationTableWriter.java
index b65743698..afce2f6c8 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/writer/ObservationTableWriter.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/observationtable/writer/ObservationTableWriter.java
@@ -23,6 +23,7 @@
 import de.learnlib.datastructure.observationtable.ObservationTable;
 import net.automatalib.common.util.IOUtil;
 
+@FunctionalInterface
 public interface ObservationTableWriter<I, D> {
 
     void write(ObservationTable<? extends I, ? extends D> table, Appendable out) throws IOException;
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/AbstractBlueFringePTAState.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/AbstractBlueFringePTAState.java
index b4da79886..2c69bd784 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/AbstractBlueFringePTAState.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/AbstractBlueFringePTAState.java
@@ -18,6 +18,10 @@
 import net.automatalib.common.util.comparison.CmpUtil;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
+/**
+ * Note: this class has a natural ordering that is inconsistent with equals.
+ */
+@SuppressWarnings("PMD.OverrideBothEqualsAndHashCodeOnComparable")
 public abstract class AbstractBlueFringePTAState<S extends AbstractBlueFringePTAState<S, SP, TP>, SP, TP>
         extends AbstractBasePTAState<S, SP, TP> implements Comparable<S> {
 
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/config/ProcessingOrder.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/config/ProcessingOrder.java
index a4bfbe74c..1e2729ffa 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/config/ProcessingOrder.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/config/ProcessingOrder.java
@@ -32,6 +32,7 @@
  *
  * @see DefaultProcessingOrders
  */
+@FunctionalInterface
 public interface ProcessingOrder {
 
     /**
diff --git a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/visualization/PTAVisualizationHelper.java b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/visualization/PTAVisualizationHelper.java
index 7a8ca0e64..9ffa8a89e 100644
--- a/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/visualization/PTAVisualizationHelper.java
+++ b/commons/datastructures/src/main/java/de/learnlib/datastructure/pta/visualization/PTAVisualizationHelper.java
@@ -36,8 +36,8 @@ public boolean getEdgeProperties(S src,
                                      Map<String, String> properties) {
         super.getEdgeProperties(src, edge, tgt, properties);
 
-        final I input = edge.getInput();
-        properties.put(EdgeAttrs.LABEL, input + " / " + automaton.getTransitionProperty(edge.getTransition()));
+        final I input = edge.input();
+        properties.put(EdgeAttrs.LABEL, input + " / " + automaton.getTransitionProperty(edge.transition()));
 
         return true;
     }
diff --git a/commons/settings/src/main/java/de/learnlib/setting/LearnLibSettingsSource.java b/commons/settings/src/main/java/de/learnlib/setting/LearnLibSettingsSource.java
index d97e3ee01..166aa0b51 100644
--- a/commons/settings/src/main/java/de/learnlib/setting/LearnLibSettingsSource.java
+++ b/commons/settings/src/main/java/de/learnlib/setting/LearnLibSettingsSource.java
@@ -17,4 +17,5 @@
 
 import net.automatalib.common.util.setting.SettingsSource;
 
+@FunctionalInterface
 public interface LearnLibSettingsSource extends SettingsSource {}
diff --git a/drivers/basic/src/main/java/de/learnlib/driver/reflect/Error.java b/drivers/basic/src/main/java/de/learnlib/driver/reflect/Error.java
index fe80cab2d..54a1ca6fe 100644
--- a/drivers/basic/src/main/java/de/learnlib/driver/reflect/Error.java
+++ b/drivers/basic/src/main/java/de/learnlib/driver/reflect/Error.java
@@ -39,15 +39,7 @@ public int hashCode() {
 
     @Override
     public boolean equals(@Nullable Object obj) {
-        if (this == obj) {
-            return true;
-        }
-        if (!(obj instanceof Error)) {
-            return false;
-        }
-
-        final Error other = (Error) obj;
-        return Objects.equals(this.id, other.id);
+        return this == obj || obj instanceof Error other && Objects.equals(this.id, other.id);
     }
 
     @Override
diff --git a/drivers/basic/src/main/java/de/learnlib/driver/reflect/InstanceConstructor.java b/drivers/basic/src/main/java/de/learnlib/driver/reflect/InstanceConstructor.java
index bf347708b..b9beaf9af 100644
--- a/drivers/basic/src/main/java/de/learnlib/driver/reflect/InstanceConstructor.java
+++ b/drivers/basic/src/main/java/de/learnlib/driver/reflect/InstanceConstructor.java
@@ -31,7 +31,6 @@ final class InstanceConstructor implements ContextHandler<Object> {
         this.params = params;
     }
 
-    @SuppressWarnings("PMD.PreserveStackTrace")
     @Override
     public Object createContext() {
         try {
diff --git a/drivers/basic/src/main/java/de/learnlib/driver/reflect/MethodInput.java b/drivers/basic/src/main/java/de/learnlib/driver/reflect/MethodInput.java
index 9c220ea27..d35beda8b 100644
--- a/drivers/basic/src/main/java/de/learnlib/driver/reflect/MethodInput.java
+++ b/drivers/basic/src/main/java/de/learnlib/driver/reflect/MethodInput.java
@@ -36,7 +36,6 @@ public MethodInput(String displayName, Method method, Object[] parameters) {
         this.parameters = parameters;
     }
 
-    @SuppressWarnings("PMD.PreserveStackTrace")
     @Override
     public MethodOutput execute(Object context) {
         try {
diff --git a/drivers/basic/src/main/java/de/learnlib/driver/reflect/ReturnValue.java b/drivers/basic/src/main/java/de/learnlib/driver/reflect/ReturnValue.java
index 6ba36534e..2fb55346d 100644
--- a/drivers/basic/src/main/java/de/learnlib/driver/reflect/ReturnValue.java
+++ b/drivers/basic/src/main/java/de/learnlib/driver/reflect/ReturnValue.java
@@ -40,15 +40,7 @@ public int hashCode() {
 
     @Override
     public boolean equals(@Nullable Object obj) {
-        if (this == obj) {
-            return true;
-        }
-        if (!(obj instanceof ReturnValue)) {
-            return false;
-        }
-
-        final ReturnValue<?> other = (ReturnValue<?>) obj;
-        return Objects.equals(this.ret, other.ret);
+        return this == obj || obj instanceof ReturnValue<?> other && Objects.equals(this.ret, other.ret);
     }
 
     @Override
diff --git a/drivers/mapper/src/test/java/de/learnlib/mapper/SULMapperCompositionTest.java b/drivers/mapper/src/test/java/de/learnlib/mapper/SULMapperCompositionTest.java
index d1370c630..ba3725909 100644
--- a/drivers/mapper/src/test/java/de/learnlib/mapper/SULMapperCompositionTest.java
+++ b/drivers/mapper/src/test/java/de/learnlib/mapper/SULMapperCompositionTest.java
@@ -126,16 +126,12 @@ public void post() {}
 
         @Override
         public Character step(Character in) {
-            switch (in) {
-                case OUTER_EXCEPTION_TRIGGER_CHAR:
-                    throw new OuterWrappedException(new IllegalArgumentException());
-                case INNER_EXCEPTION_TRIGGER_CHAR:
-                    throw new InnerUnwrappedException();
-                case NESTED_EXCEPTION_TRIGGER_CHAR:
-                    throw new NestedUnwrappedException();
-                default:
-                    return in;
-            }
+            return switch (in) {
+                case OUTER_EXCEPTION_TRIGGER_CHAR -> throw new OuterWrappedException(new IllegalArgumentException());
+                case INNER_EXCEPTION_TRIGGER_CHAR -> throw new InnerUnwrappedException();
+                case NESTED_EXCEPTION_TRIGGER_CHAR -> throw new NestedUnwrappedException();
+                default -> in;
+            };
         }
     }
 
diff --git a/examples/pom.xml b/examples/pom.xml
index b69ee71f8..1afeacbc7 100644
--- a/examples/pom.xml
+++ b/examples/pom.xml
@@ -193,12 +193,35 @@ limitations under the License.
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-surefire-plugin</artifactId>
+                    <!-- For some reason (probably due to the testing dependencies) surefire auto-detects a JUnit runner.
+                         Since we use testng exclusively, help the plugin a little bit -->
+                    <dependencies>
+                        <dependency>
+                            <groupId>org.apache.maven.surefire</groupId>
+                            <artifactId>surefire-testng</artifactId>
+                            <version>${surefire-plugin.version}</version>
+                        </dependency>
+                    </dependencies>
                     <configuration>
                         <systemPropertyVariables>
-                            <awt.toolkit>com.github.caciocavallosilano.cacio.ctc.CTCToolkit</awt.toolkit>
-                            <java.awt.graphicsenv>com.github.caciocavallosilano.cacio.ctc.CTCGraphicsEnvironment</java.awt.graphicsenv>
                             <java.awt.headless>false</java.awt.headless>
                         </systemPropertyVariables>
+                        <argLine>
+                            @{argLine}
+                            --add-exports=java.desktop/java.awt=ALL-UNNAMED
+                            --add-exports=java.desktop/java.awt.peer=ALL-UNNAMED
+                            --add-exports=java.desktop/sun.awt.image=ALL-UNNAMED
+                            --add-exports=java.desktop/sun.java2d=ALL-UNNAMED
+                            --add-exports=java.desktop/java.awt.dnd.peer=ALL-UNNAMED
+                            --add-exports=java.desktop/sun.awt=ALL-UNNAMED
+                            --add-exports=java.desktop/sun.awt.event=ALL-UNNAMED
+                            --add-exports=java.desktop/sun.awt.datatransfer=ALL-UNNAMED
+                            --add-exports=java.base/sun.security.action=ALL-UNNAMED
+                            --add-opens=java.base/java.util=ALL-UNNAMED
+                            --add-opens=java.desktop/java.awt=ALL-UNNAMED
+                            --add-opens=java.desktop/sun.java2d=ALL-UNNAMED
+                            --add-opens=java.base/java.lang.reflect=ALL-UNNAMED
+                        </argLine>
                     </configuration>
                 </plugin>
             </plugins>
diff --git a/examples/src/main/java/de/learnlib/example/Example3.java b/examples/src/main/java/de/learnlib/example/Example3.java
index acae7bc26..c73da80a8 100644
--- a/examples/src/main/java/de/learnlib/example/Example3.java
+++ b/examples/src/main/java/de/learnlib/example/Example3.java
@@ -161,16 +161,14 @@ public static void main(String[] args) {
     }
 
     private @Nullable String exec(BoundedStringQueue s, String input) {
-        switch (input) {
-            case OFFER_1:
-            case OFFER_2:
+        return switch (input) {
+            case OFFER_1, OFFER_2 -> {
                 s.offer(input);
-                return "void";
-            case POLL:
-                return s.poll();
-            default:
-                throw new IllegalArgumentException("unknown input symbol");
-        }
+                yield "void";
+            }
+            case POLL -> s.poll();
+            default -> throw new IllegalArgumentException("unknown input symbol");
+        };
     }
 
     /**
diff --git a/examples/src/main/java/de/learnlib/example/aaar/AlternatingBitExampleExplicit.java b/examples/src/main/java/de/learnlib/example/aaar/AlternatingBitExampleExplicit.java
index c3588db6a..c0c127b74 100644
--- a/examples/src/main/java/de/learnlib/example/aaar/AlternatingBitExampleExplicit.java
+++ b/examples/src/main/java/de/learnlib/example/aaar/AlternatingBitExampleExplicit.java
@@ -127,14 +127,11 @@ public String getAbstractSymbol(Event c) {
 
         @Override
         public Event getRepresentative(String a) {
-            switch (a) {
-                case "recv":
-                    return new Recv();
-                case "msg":
-                    return new Msg<>(0, "d");
-                default:
-                    throw new IllegalArgumentException("Unknown abstract: " + a);
-            }
+            return switch (a) {
+                case "recv" -> new Recv();
+                case "msg" -> new Msg<>(0, "d");
+                default -> throw new IllegalArgumentException("Unknown abstract: " + a);
+            };
         }
 
         @Override
diff --git a/examples/src/main/java/de/learnlib/example/aaar/Event.java b/examples/src/main/java/de/learnlib/example/aaar/Event.java
index 31b239ba9..c04946c9c 100644
--- a/examples/src/main/java/de/learnlib/example/aaar/Event.java
+++ b/examples/src/main/java/de/learnlib/example/aaar/Event.java
@@ -38,12 +38,8 @@ public String toString() {
 
         @Override
         public boolean equals(@Nullable Object o) {
-            if (!(o instanceof Msg)) {
-                return false;
-            }
-            final Msg<?> that = (Msg<?>) o;
-
-            return this.seq == that.seq && Objects.equals(this.data, that.data);
+            return this == o ||
+                   o instanceof Msg<?> that && this.seq == that.seq && Objects.equals(this.data, that.data);
         }
 
         @Override
diff --git a/examples/src/main/java/de/learnlib/example/aaar/Protocol.java b/examples/src/main/java/de/learnlib/example/aaar/Protocol.java
index bc6fc19cd..097a24ac5 100644
--- a/examples/src/main/java/de/learnlib/example/aaar/Protocol.java
+++ b/examples/src/main/java/de/learnlib/example/aaar/Protocol.java
@@ -41,15 +41,12 @@ private void reset() {
     }
 
     private String handleEvent(Event event) {
-        if (event instanceof Msg<?>) {
-            Msg<?> msg = (Msg<?>) event;
-
+        if (event instanceof Msg<?> msg) {
             if (buffer == null && msg.seq % 2 == seqExp % 2) {
                 buffer = msg.data;
                 seqExp++;
                 return "ind";
             }
-
             return "-";
         } else if (event instanceof Recv) {
             if (buffer == null) {
diff --git a/examples/src/test/java/de/learnlib/example/ExamplesTest.java b/examples/src/test/java/de/learnlib/example/ExamplesTest.java
index 92324bbeb..f1491d23d 100644
--- a/examples/src/test/java/de/learnlib/example/ExamplesTest.java
+++ b/examples/src/test/java/de/learnlib/example/ExamplesTest.java
@@ -25,6 +25,7 @@
 
 import javax.swing.SwingUtilities;
 
+import com.github.caciocavallosilano.cacio.ctc.junit.CacioExtension;
 import de.learnlib.example.aaar.AlternatingBitExampleExplicit;
 import de.learnlib.example.aaar.AlternatingBitExampleGeneric;
 import net.automatalib.modelchecker.ltsmin.LTSminUtil;
@@ -40,6 +41,9 @@ public class ExamplesTest {
     @BeforeClass
     public void setupAutoClose() {
         if (isJVMCompatible()) {
+            // hack: the static initializer of this class does the magic we want, so only invoke it on compatible JVMs
+            new CacioExtension();
+
             // As soon as we observe an event that indicates a new window, close it to prevent blocking the tests.
             Toolkit.getDefaultToolkit().addAWTEventListener(event -> {
                 final WindowEvent windowEvent = (WindowEvent) event;
@@ -173,12 +177,13 @@ public void testExample3() throws InvocationTargetException, InterruptedExceptio
     }
 
     private static boolean isJVMCompatible() {
-        return Runtime.version().feature() == 11;
+        final int feature = Runtime.version().feature();
+        return feature == 17 || feature == 21;
     }
 
     private static void requireJVMCompatibility() {
-        if (Runtime.version().feature() != 11) {
-            throw new SkipException("The headless AWT environment currently only works with Java 11 or <=8");
+        if (!isJVMCompatible()) {
+            throw new SkipException("The headless AWT environment only works with specific JVM versions");
         }
     }
 
diff --git a/filters/cache/src/main/java/de/learnlib/filter/cache/LearningCache.java b/filters/cache/src/main/java/de/learnlib/filter/cache/LearningCache.java
index cf6a862a9..9f6b13244 100644
--- a/filters/cache/src/main/java/de/learnlib/filter/cache/LearningCache.java
+++ b/filters/cache/src/main/java/de/learnlib/filter/cache/LearningCache.java
@@ -40,6 +40,7 @@
  * @param <O>
  *         output symbol type
  */
+@FunctionalInterface
 public interface LearningCache<A, I, O> {
 
     /**
@@ -59,6 +60,7 @@ public interface LearningCache<A, I, O> {
      * @param <I>
      *         input symbol type
      */
+    @FunctionalInterface
     interface DFALearningCache<I> extends LearningCache<DFA<?, I>, I, Boolean> {}
 
     /**
@@ -69,6 +71,7 @@ interface DFALearningCache<I> extends LearningCache<DFA<?, I>, I, Boolean> {}
      * @param <O>
      *         output symbol type
      */
+    @FunctionalInterface
     interface MealyLearningCache<I, O> extends LearningCache<MealyMachine<?, I, ?, O>, I, Word<O>> {}
 
     /**
@@ -79,5 +82,6 @@ interface MealyLearningCache<I, O> extends LearningCache<MealyMachine<?, I, ?, O
      * @param <O>
      *         output symbol type
      */
+    @FunctionalInterface
     interface MooreLearningCache<I, O> extends LearningCache<MooreMachine<?, I, ?, O>, I, Word<O>> {}
 }
diff --git a/filters/cache/src/main/java/de/learnlib/filter/cache/mealy/AdaptiveQueryCache.java b/filters/cache/src/main/java/de/learnlib/filter/cache/mealy/AdaptiveQueryCache.java
index 1c1c94490..4fdc24465 100644
--- a/filters/cache/src/main/java/de/learnlib/filter/cache/mealy/AdaptiveQueryCache.java
+++ b/filters/cache/src/main/java/de/learnlib/filter/cache/mealy/AdaptiveQueryCache.java
@@ -276,15 +276,14 @@ public Response processOutput(O out) {
 
             final Response response = delegate.processOutput(out);
 
-            switch (response) {
-                case FINISHED:
+            return switch (response) {
+                case FINISHED -> {
                     isFinished = true;
-                    return Response.FINISHED;
-                case RESET:
-                    return Response.FINISHED;
-                default:
-                    return response;
-            }
+                    yield Response.FINISHED;
+                }
+                case RESET -> Response.FINISHED;
+                case SYMBOL -> response;
+            };
         }
     }
 
diff --git a/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/BoundedDeque.java b/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/BoundedDeque.java
index 7a147e2ae..475b1e3f9 100644
--- a/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/BoundedDeque.java
+++ b/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/BoundedDeque.java
@@ -100,14 +100,11 @@ public BoundedDeque(int capacity, AccessPolicy accessPolicy, EvictPolicy evictPo
      * @return the evicted element, may be {@code null} if the queue was empty
      */
     private @Nullable E evict() {
-        switch (evictPolicy) {
-            case EVICT_OLDEST:
-                return deque.pollFirst();
-            case EVICT_NEWEST:
-                return deque.pollLast();
-            default:
-                throw new IllegalStateException("Illegal evict policy: " + evictPolicy);
-        }
+        return switch (evictPolicy) {
+            case EVICT_OLDEST -> deque.pollFirst();
+            case EVICT_NEWEST -> deque.pollLast();
+            default -> throw new IllegalStateException("Illegal evict policy: " + evictPolicy);
+        };
     }
 
     /**
@@ -117,14 +114,10 @@ public BoundedDeque(int capacity, AccessPolicy accessPolicy, EvictPolicy evictPo
      * @return the evicted element, may be {@code null} if the queue was empty
      */
     public @Nullable E retrieve() {
-        switch (accessPolicy) {
-            case LIFO:
-                return deque.pollLast();
-            case FIFO:
-                return deque.pollFirst();
-            default:
-                throw new IllegalStateException("Illegal evict policy: " + evictPolicy);
-        }
+        return switch (accessPolicy) {
+            case LIFO -> deque.pollLast();
+            case FIFO -> deque.pollFirst();
+        };
     }
 
     /**
@@ -134,14 +127,10 @@ public BoundedDeque(int capacity, AccessPolicy accessPolicy, EvictPolicy evictPo
      * @return the top-most element of the container
      */
     public @Nullable E peek() {
-        switch (accessPolicy) {
-            case LIFO:
-                return deque.peekLast();
-            case FIFO:
-                return deque.peekFirst();
-            default:
-                throw new IllegalStateException("Illegal evict policy: " + evictPolicy);
-        }
+        return switch (accessPolicy) {
+            case LIFO -> deque.peekLast();
+            case FIFO -> deque.peekFirst();
+        };
     }
 
     /**
diff --git a/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/SystemStateHandler.java b/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/SystemStateHandler.java
index d3e48d6ef..7db0f174f 100644
--- a/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/SystemStateHandler.java
+++ b/filters/reuse/src/main/java/de/learnlib/filter/reuse/tree/SystemStateHandler.java
@@ -31,6 +31,7 @@
  * @param <S>
  *         system state class
  */
+@FunctionalInterface
 public interface SystemStateHandler<S> {
 
     /**
diff --git a/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWMethodEQOracle.java b/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWMethodEQOracle.java
index a8e201797..7cba476b0 100644
--- a/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWMethodEQOracle.java
+++ b/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWMethodEQOracle.java
@@ -186,6 +186,7 @@ public RandomWMethodEQOracle(MembershipOracle<I, D> sulOracle,
 
     @Override
     public Stream<Word<I>> generateTestWords(A hypothesis, Collection<? extends I> inputs) {
+        // explicitly assign type to (redundant) variable, otherwise javac complains
         UniversalDeterministicAutomaton<?, I, ?, ?, ?> aut = hypothesis;
         return doGenerateTestWords(aut, inputs);
     }
diff --git a/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWpMethodEQOracle.java b/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWpMethodEQOracle.java
index f6310b642..2b525f98a 100644
--- a/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWpMethodEQOracle.java
+++ b/oracles/equivalence-oracles/src/main/java/de/learnlib/oracle/equivalence/RandomWpMethodEQOracle.java
@@ -187,6 +187,7 @@ public RandomWpMethodEQOracle(MembershipOracle<I, D> sulOracle,
 
     @Override
     public Stream<Word<I>> generateTestWords(A hypothesis, Collection<? extends I> inputs) {
+        // explicitly assign type to (redundant) variable, otherwise javac complains
         UniversalDeterministicAutomaton<?, I, ?, ?, ?> aut = hypothesis;
         return doGenerateTestWords(aut, inputs);
     }
diff --git a/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractDynamicBatchProcessorBuilder.java b/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractDynamicBatchProcessorBuilder.java
index f951cbb5f..97c9b3d10 100644
--- a/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractDynamicBatchProcessorBuilder.java
+++ b/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractDynamicBatchProcessorBuilder.java
@@ -144,16 +144,10 @@ public OR create() {
         if (customExecutor != null) {
             executor = customExecutor;
         } else {
-            switch (poolPolicy) {
-                case FIXED:
-                    executor = Executors.newFixedThreadPool(size);
-                    break;
-                case CACHED:
-                    executor = new ScalingThreadPoolExecutor(0, size, DEFAULT_KEEP_ALIVE_TIME, TimeUnit.SECONDS);
-                    break;
-                default:
-                    throw new IllegalStateException("Unknown pool policy: " + poolPolicy);
-            }
+            executor = switch (poolPolicy) {
+                case FIXED -> Executors.newFixedThreadPool(size);
+                case CACHED -> new ScalingThreadPoolExecutor(0, size, DEFAULT_KEEP_ALIVE_TIME, TimeUnit.SECONDS);
+            };
         }
 
         return buildOracle(supplier, batchSize, executor);
diff --git a/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractStaticBatchProcessorBuilder.java b/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractStaticBatchProcessorBuilder.java
index 9c675df33..734a927ca 100644
--- a/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractStaticBatchProcessorBuilder.java
+++ b/oracles/parallelism/src/main/java/de/learnlib/oracle/parallelism/AbstractStaticBatchProcessorBuilder.java
@@ -142,16 +142,10 @@ public OR create() {
         if (customExecutor != null) {
             executor = customExecutor;
         } else {
-            switch (poolPolicy) {
-                case FIXED:
-                    executor = Executors.newFixedThreadPool(size);
-                    break;
-                case CACHED:
-                    executor = new ScalingThreadPoolExecutor(0, size, DEFAULT_KEEP_ALIVE_TIME, TimeUnit.SECONDS);
-                    break;
-                default:
-                    throw new IllegalStateException("Unknown pool policy: " + poolPolicy);
-            }
+            executor = switch (poolPolicy) {
+                case FIXED -> Executors.newFixedThreadPool(size);
+                case CACHED -> new ScalingThreadPoolExecutor(0, size, DEFAULT_KEEP_ALIVE_TIME, TimeUnit.SECONDS);
+            };
         }
 
         return buildOracle(instances, minBatchSize, executor);
diff --git a/pom.xml b/pom.xml
index 6245bdfce..be377bbef 100644
--- a/pom.xml
+++ b/pom.xml
@@ -213,9 +213,9 @@ limitations under the License.
         <!-- general config -->
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
-        <maven.compiler.source>11</maven.compiler.source>
-        <maven.compiler.target>11</maven.compiler.target>
-        <maven.compiler.release>11</maven.compiler.release>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <maven.compiler.release>17</maven.compiler.release>
         <argLine /> <!-- compatibility for property expansion in surefire-plugin -->
 
         <!-- plugin versions -->
@@ -235,32 +235,32 @@ limitations under the License.
         <info-reports-plugin.version>3.8.0</info-reports-plugin.version>
         <install-plugin.version>3.1.3</install-plugin.version>
         <invoker-plugin.version>3.9.0</invoker-plugin.version>
-        <jacoco-plugin.version>0.8.12</jacoco-plugin.version>
+        <jacoco-plugin.version>0.8.13</jacoco-plugin.version>
         <jar-plugin.version>3.4.2</jar-plugin.version>
         <javadoc-plugin.version>3.11.2</javadoc-plugin.version>
         <lifecycle-mapping.version>1.0.0</lifecycle-mapping.version>
-        <pmd-plugin.version>3.26.0</pmd-plugin.version>
+        <pmd-plugin.version>3.28.0</pmd-plugin.version>
         <release-plugin.version>3.1.0</release-plugin.version>
         <resources-plugin.version>3.3.1</resources-plugin.version>
         <scm-publish-plugin.version>3.3.0</scm-publish-plugin.version>
         <site-plugin.version>3.21.0</site-plugin.version>
         <source-plugin.version>3.3.1</source-plugin.version>
-        <spotbugs-plugin.version>4.8.6.6</spotbugs-plugin.version>
+        <spotbugs-plugin.version>4.9.8.1</spotbugs-plugin.version>
         <surefire-plugin.version>3.5.2</surefire-plugin.version>
         <tidy-pom.version>1.3.0</tidy-pom.version>
 
         <!-- dependency versions -->
         <automatalib.version>0.13.0-SNAPSHOT</automatalib.version>
         <build-tools.version>0.1.1</build-tools.version>
-        <cacio.version>1.11.1</cacio.version>
+        <cacio.version>1.18</cacio.version>
         <checkerframework.version>3.48.3</checkerframework.version>
         <checkstyle.version>10.21.1</checkstyle.version>
-        <extra-enforcer-rules.version>1.7.0</extra-enforcer-rules.version>
+        <extra-enforcer-rules.version>1.10.0</extra-enforcer-rules.version>
         <fury.version>0.9.0</fury.version>
         <jaxb-api.version>2.3.1</jaxb-api.version>
         <logback.version>1.5.15</logback.version>
         <metainf-services.version>1.11</metainf-services.version>
-        <mockito.version>5.14.2</mockito.version>
+        <mockito.version>5.20.0</mockito.version>
         <slf4j.version>2.0.16</slf4j.version>
         <testng.version>7.10.2</testng.version>
 
@@ -1217,15 +1217,6 @@ limitations under the License.
                 </plugins>
             </build>
         </profile>
-        <profile>
-            <id>jdk17-compat</id>
-            <activation>
-                <jdk>17</jdk>
-            </activation>
-            <properties>
-                <cacio.version>1.17.3</cacio.version>
-            </properties>
-        </profile>
         <profile>
             <!-- define module in a profile so that we can disable it during a release -->
             <id>examples</id>
diff --git a/test-support/learner-it-support/src/main/java/de/learnlib/testsupport/it/learner/PassiveLearnerVariantList.java b/test-support/learner-it-support/src/main/java/de/learnlib/testsupport/it/learner/PassiveLearnerVariantList.java
index d47f156b6..67c894dd2 100644
--- a/test-support/learner-it-support/src/main/java/de/learnlib/testsupport/it/learner/PassiveLearnerVariantList.java
+++ b/test-support/learner-it-support/src/main/java/de/learnlib/testsupport/it/learner/PassiveLearnerVariantList.java
@@ -22,6 +22,7 @@
 import net.automatalib.automaton.transducer.SubsequentialTransducer;
 import net.automatalib.word.Word;
 
+@FunctionalInterface
 public interface PassiveLearnerVariantList<M, I, D> {
 
     /**
@@ -37,12 +38,16 @@ public interface PassiveLearnerVariantList<M, I, D> {
      */
     void addLearnerVariant(String name, PassiveLearningAlgorithm<? extends M, I, D> learner);
 
+    @FunctionalInterface
     interface DFALearnerVariantList<I> extends PassiveLearnerVariantList<DFA<?, I>, I, Boolean> {}
 
+    @FunctionalInterface
     interface MealyLearnerVariantList<I, O> extends PassiveLearnerVariantList<MealyMachine<?, I, ?, O>, I, Word<O>> {}
 
+    @FunctionalInterface
     interface MooreLearnerVariantList<I, O> extends PassiveLearnerVariantList<MooreMachine<?, I, ?, O>, I, Word<O>> {}
 
+    @FunctionalInterface
     interface SSTLearnerVariantList<I, O>
             extends PassiveLearnerVariantList<SubsequentialTransducer<?, I, ?, O>, I, Word<O>> {}
 }
diff --git a/test-support/learning-examples/src/main/java/de/learnlib/testsupport/example/PassiveLearningExample.java b/test-support/learning-examples/src/main/java/de/learnlib/testsupport/example/PassiveLearningExample.java
index 08e3dfc91..6dab3bb83 100644
--- a/test-support/learning-examples/src/main/java/de/learnlib/testsupport/example/PassiveLearningExample.java
+++ b/test-support/learning-examples/src/main/java/de/learnlib/testsupport/example/PassiveLearningExample.java
@@ -20,15 +20,20 @@
 import de.learnlib.query.DefaultQuery;
 import net.automatalib.word.Word;
 
+@FunctionalInterface
 public interface PassiveLearningExample<I, D> {
 
     Collection<DefaultQuery<I, D>> getSamples();
 
+    @FunctionalInterface
     interface DFAPassiveLearningExample<I> extends PassiveLearningExample<I, Boolean> {}
 
+    @FunctionalInterface
     interface MealyPassiveLearningExample<I, O> extends PassiveLearningExample<I, Word<O>> {}
 
+    @FunctionalInterface
     interface MoorePassiveLearningExample<I, O> extends PassiveLearningExample<I, Word<O>> {}
 
+    @FunctionalInterface
     interface SSTPassiveLearningExample<I, O> extends PassiveLearningExample<I, Word<O>> {}
 }
diff --git a/test-support/test-support/src/main/java/de/learnlib/testsupport/AbstractBFOracleTest.java b/test-support/test-support/src/main/java/de/learnlib/testsupport/AbstractBFOracleTest.java
index 0b7a187c8..8d6bacf32 100644
--- a/test-support/test-support/src/main/java/de/learnlib/testsupport/AbstractBFOracleTest.java
+++ b/test-support/test-support/src/main/java/de/learnlib/testsupport/AbstractBFOracleTest.java
@@ -47,7 +47,6 @@ public void setUp() {
     }
 
     @AfterMethod
-    @SuppressWarnings("PMD.SignatureDeclareThrowsException")
     public void tearDown() throws Exception {
         this.mock.close();
     }