Add Java 17 test class ... (#17)

- Strongly Encapsulated JDK Internals
- Switch Pattern Matching
- Random Generator Factory
- Hex Formatting and Parsing Utility

Author: mperor

README.md

@@ -28,5 +28,6 @@ This project includes unit tests for key functionalities introduced in each Java
 - [Java 14](src/test/java/pl/mperor/lab/java/Java14.java)
 - [Java 15](src/test/java/pl/mperor/lab/java/Java15.java)
 - [Java 16](src/test/java/pl/mperor/lab/java/Java16.java)
+- [Java 17](src/test/java/pl/mperor/lab/java/Java17.java)
 
 For detailed examples and tests of each feature, please refer to the individual source files linked above.

src/test/java/pl/mperor/lab/java/Java17.java

@@ -0,0 +1,78 @@
+package pl.mperor.lab.java;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.InaccessibleObjectException;
+import java.util.HexFormat;
+import java.util.ServiceLoader;
+import java.util.random.RandomGenerator;
+import java.util.random.RandomGeneratorFactory;
+
+/**
+ * Java 17 (September 2021)
+ */
+public class Java17 {
+
+    @Test
+    public void testStronglyEncapsulatedInternals() {
+        Assertions.assertThrows(InaccessibleObjectException.class, () -> deepLookIntoStringBytes("Hello"));
+    }
+
+    private static byte[] deepLookIntoStringBytes(String string) throws IllegalAccessException, NoSuchFieldException {
+        Field valueField = String.class.getDeclaredField("value");
+        valueField.setAccessible(true);
+        return (byte[]) valueField.get(string);
+    }
+
+    @Test
+    public void testSwitchPatternMatching() {
+        Assertions.assertEquals("String: Hello", switchOverClasses("Hello"));
+        Assertions.assertEquals("int: 1", switchOverClasses(1));
+        Assertions.assertEquals("long: 13", switchOverClasses(13L));
+        Assertions.assertEquals("boolean: true", switchOverClasses(true));
+        Assertions.assertEquals("null", switchOverClasses(null));
+        record Person(String name, String surname) {
+            @Override
+            public String toString() {
+                return "%s %s".formatted(name, surname);
+            }
+        }
+        Assertions.assertEquals("Object: John Doe", switchOverClasses(new Person("John", "Doe")));
+    }
+
+    private static String switchOverClasses(Object obj) {
+        return switch (obj) {
+            case String s -> String.format("String: %s", s);
+            case Integer i -> String.format("int: %d", i);
+            case Long l -> String.format("long: %d", l);
+            case Boolean b -> String.format("boolean: %s", b);
+            case null -> "null";
+            default -> "Object: " + obj;
+        };
+    }
+
+    @Test
+    public void testRandomGeneratorFactory() {
+        var generators = ServiceLoader.load(RandomGenerator.class).stream()
+                .map(provider -> provider.type().getCanonicalName())
+                .peek(System.out::println)
+                .toList();
+
+        Assertions.assertTrue(generators.contains("java.util.Random"));
+        var defaultRandomGenerator = RandomGeneratorFactory.getDefault().create();
+        Assertions.assertEquals("jdk.random.L32X64MixRandom", defaultRandomGenerator.getClass().getCanonicalName());
+    }
+
+    @Test
+    void testHexFormat() {
+        HexFormat hexFormat = HexFormat.of();
+        String hex = hexFormat.formatHex(new byte[]{0x1A, 0x2B, 0x3C});
+        Assertions.assertEquals("1a2b3c", hex);
+        Assertions.assertArrayEquals(new byte[]{0x1A, 0x2B, 0x3C}, hexFormat.parseHex(hex));
+        Assertions.assertFalse(HexFormat.isHexDigit('g'));
+        Assertions.assertEquals(16 + 10, HexFormat.fromHexDigits("1a"));
+    }
+
+}