Java实现一个基于LRU时间复杂度为O(1)的缓存的方法

public class LruCache<K,V> {
	/** 这里简单点直接初始化了*/
  private int capacity = 2;
  private int size = 0;
  private HashMap<K,DoubleListNode<K,V>> cache = new HashMap<>(capacity);
  private DoubleListNode<K,V> lruNode = new DoubleListNode<K, V>(null,null,null,null);
  private DoubleListNode<K,V> mruNode = new DoubleListNode<K, V>(null,null,null,null);

  public V get(K key){
    DoubleListNode<K,V> target = cache.get(key);
    if (target == null) {
      return null;
    }
    /** 使用过就移动到右侧 */
    move2mru(target);
    return target.value;
  }

  public void put(K key,V value){
    if(cache.containsKey(key)){
      DoubleListNode<K,V> temp = cache.get(key);
      temp.value = value;
      /** 使用过就移动到右侧 */
      move2mru(temp);
      return;
    }

		/** 容量满了清除左侧 */
    if(size >= capacity){
      evict4lru();
    }
    DoubleListNode<K,V> newNode = new DoubleListNode<>(mruNode,null,key,value);
    if(size == 0){
      lruNode.next = newNode;
    }
    mruNode.next = newNode;
    mruNode = newNode;
    cache.put(key,newNode);
    size++;
  }

  private void move2mru(DoubleListNode<K,V> newMru){
    DoubleListNode<K,V> pre = newMru.pre;
    DoubleListNode<K,V> next = newMru.next;
    pre.next = next;
    newMru.pre = mruNode;
    mruNode.next = newMru;
    mruNode = newMru;
  }

  private void evict4lru(){
  	cache.remove(lruNode.next.key);
    lruNode.next = lruNode.next.next;
    size--;
  }

  public String toString(){
    StringBuffer sb = new StringBuffer("lru -> ");
    DoubleListNode<K,V> temp = lruNode;
    while(temp!=null){
      sb.append(temp.key).append(":").append(temp.value);
      sb.append(" -> ");
      temp = temp.next;
    }
    sb.append(" -> mru ");
    return sb.toString();
  }

  public static void main(String[] args) {
    LruCache<String,String> cache = new LruCache<>();
    cache.put("1","1");
    System.out.println(cache);
    cache.get("1");
    cache.put("2","2");
    System.out.println(cache);
    cache.put("3","3");
    System.out.println(cache);
    cache.put("4","4");
    System.out.println(cache);
  }
}

class DoubleListNode<K,V>{
  K key;
  V value;
  DoubleListNode<K,V> pre;
  DoubleListNode<K,V> next;

  public DoubleListNode(K key,V value){
    this.key = key;
    this.value = value;
  }

  public DoubleListNode(DoubleListNode<K,V> pre,DoubleListNode<K,V> next,K key,V value){
    this.pre = pre;
    this.next = next;
    this.key = key;
    this.value = value;
  }
}