java LRU算法介绍与用法示例

 public class LRUByHashMap { /* * 通过LinkHashMap简单实现LRU算法 */ /** * 缓存大小 */ private int cacheSize; /** * 当前缓存数目 */ private int currentSize; private LinkedHashMap maps; public LRUByHashMap(int cacheSize1) { this.cacheSize = cacheSize1; maps = new LinkedHashMap() { /** * */ private static final long serialVersionUID = 1; // 这里移除旧的缓存数据 @Override protected boolean removeEldestEntry(java.util.Map.Entry eldest) { // 当超过缓存数量的时候就将旧的数据移除 return getCurrentSize() > LRUByHashMap.this.cacheSize; } }; } public synchronized int getCurrentSize() { return maps.size(); } public synchronized void put(K k, V v) { if (k == null) { throw new Error("存入的键值不能为空"); } maps.put(k, v); } public synchronized void remove(K k) { if (k == null) { throw new Error("移除的键值不能为空"); } maps.remove(k); } public synchronized void clear() { maps = null; } // 获取集合 public synchronized Collection getCollection() { if (maps != null) { return maps.values(); } else { return null; } } public static void main(String[] args) { // 测试 LRUByHashMap maps = new LRUByHashMap( 3); maps.put(1, "1"); maps.put(2, "2"); maps.put(3, "3"); maps.put(4, "4"); maps.put(5, "5"); maps.put(6, "6"); Collection col = maps.getCollection(); System.out.println("存入缓存中的数据是--->>" + col.toString()); } } 

 public class LRUCache { private int cacheSize; private Hashtable nodes;//缓存容器 private int currentSize; private Entry first;//链表头 private Entry last;//链表尾 public LRUCache(int i) { currentSize = 0; cacheSize = i; nodes = new Hashtable(i);//缓存容器 } /** * 获取缓存中对象,并把它放在最前面 */ public Entry get(Object key) { Entry node = nodes.get(key); if (node != null) { moveToHead(node); return node; } else { return null; } } /** * 添加 entry到hashtable, 并把entry */ public void put(Object key, Object value) { //先查看hashtable是否存在该entry, 如果存在，则只更新其value Entry node = nodes.get(key); if (node == null) { //缓存容器是否已经超过大小. if (currentSize >= cacheSize) { nodes.remove(last.key); removeLast(); } else { currentSize++; } node = new Entry(); } node.value = value; //将最新使用的节点放到链表头，表示最新使用的. node.key = key moveToHead(node); nodes.put(key, node); } /** * 将entry删除, 注意：删除操作只有在cache满了才会被执行 */ public void remove(Object key) { Entry node = nodes.get(key); //在链表中删除 if (node != null) { if (node.prev != null) { node.prev.next = node.next; } if (node.next != null) { node.next.prev = node.prev; } if (last == node) last = node.prev; if (first == node) first = node.next; } //在hashtable中删除 nodes.remove(key); } /** * 删除链表尾部节点，即使用最后 使用的entry */ private void removeLast() { //链表尾不为空,则将链表尾指向null. 删除连表尾（删除最少使用的缓存对象） if (last != null) { if (last.prev != null) last.prev.next = null; else first = null; last = last.prev; } } /** * 移动到链表头，表示这个节点是最新使用过的 */ private void moveToHead(Entry node) { if (node == first) return; if (node.prev != null) node.prev.next = node.next; if (node.next != null) node.next.prev = node.prev; if (last == node) last = node.prev; if (first != null) { node.next = first; first.prev = node; } first = node; node.prev = null; if (last == null) last = first; } /* * 清空缓存 */ public void clear() { first = null; last = null; currentSize = 0; } } class Entry { Entry prev;//前一节点 Entry next;//后一节点 Object value;//值 Object key;//键 }