Add $.createLRUCache(capacity) method in lodash module.

Author: javadev

pom.xml

@@ -157,6 +157,8 @@
                   <option>-keep public class com.github.underscore.lodash.*$Chain { *; }</option>
                   <option>-keep public class com.github.underscore.lodash.*$ParseException { *; }</option>
                   <option>-keep public class com.github.underscore.lodash.*$FetchResponse { *; }</option>
+                  <option>-keep public class com.github.underscore.lodash.*$LRUCache { *; }</option>
+                  <option>-keep public class com.github.underscore.lodash.*$Node { *; }</option>
                   <option>-keepclassmembers class * { *** newArrayList(); *** newLinkedHashSet(); *** newHashSet(java.lang.Iterable); *** newLinkedHashMap(); }</option>
                   <option>-dontnote com.github.underscore.*$ClassForName</option>
               </options>

src/main/java/com/github/underscore/lodash/$.java

@@ -2803,4 +2803,85 @@ public String uncapitalize() {
     public List<String> words() {
         return words(getString().get());
     }
+
+    public static class LRUCache<K, V> {
+        private int capacity;
+        private Map<K, Node<K, V>> map = new HashMap<K, Node<K, V>>();
+        private Node head;
+        private Node end;
+
+        public LRUCache(int capacity) {
+            this.capacity = capacity;
+        }
+
+        public V get(K key) {
+            if (map.containsKey(key)) {
+                Node<K, V> node = map.get(key);
+                remove(node);
+                setHead(node);
+                return node.value;
+            }
+            return null;
+        }
+
+        public void remove(Node node) {
+            if (node.pre != null) {
+                node.pre.next = node.next;
+            } else {
+                head = node.next;
+            }
+            if (node.next != null) {
+                node.next.pre = node.pre;
+            } else {
+                end = node.pre;
+            }
+        }
+
+        public void setHead(Node node) {
+            node.next = head;
+            node.pre = null;
+            if (head != null) {
+                head.pre = node;
+            }
+            head = node;
+            if (end == null) {
+                end = head;
+            }
+        }
+
+        public void set(K key, V value) {
+            if (map.containsKey(key)) {
+                Node<K, V> old = map.get(key);
+                old.value = value;
+                remove(old);
+                setHead(old);
+            } else {
+                Node<K, V> created = new Node<K, V>(key, value);
+                if (map.size() >= capacity) {
+                    map.remove(end.key);
+                    remove(end);
+                    setHead(created);
+                } else {
+                    setHead(created);
+                }
+                map.put(key, created);
+            }
+        }
+    }
+
+    public static class Node<K, V> {
+        private K key;
+        private V value;
+        private Node pre;
+        private Node next;
+
+        public Node(K key, V value) {
+            this.key = key;
+            this.value = value;
+        }
+    }
+
+    public static <K, V> LRUCache<K, V> createLRUCache(final int capacity) {
+        return new LRUCache<K, V>(capacity);
+    }
 }

src/test/java/com/github/underscore/lodash/MathTest.java

@@ -31,6 +31,7 @@
 import org.junit.Test;
 import static java.util.Arrays.asList;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 /**
  * Underscore library unit test.
@@ -194,6 +195,21 @@ public void sumOfInt() {
         assertEquals(34, sum);
     }
 
+    @Test
+    public void createLRUCache() {
+        new $.LRUCache<Integer, String>(0);
+        $.LRUCache<Integer, String> cache = $.createLRUCache(2);
+        cache.set(0, "Value 0");
+        assertEquals("Value 0", cache.get(0));
+        assertNull(cache.get(1));
+        cache.set(1, "Value 1");
+        assertEquals("Value 1", cache.get(1));
+        cache.set(1, "Value 1+");
+        assertEquals("Value 1+", cache.get(1));
+        cache.set(2, "Value 2");
+        assertEquals("Value 2", cache.get(2));
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     public void main() {