LRU实现

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import java.util.HashMap;
import java.util.Map;

/**

• @author

• @date 2020/3/11 17:46

• @desc
  */
  public class DoubleLink {
  LRUNode head;
  LRUNode tail;

  int capacity;
  Map map;

  public DoubleLink(int capacity) {
  super();
  this.capacity = capacity;
  map = new HashMap<>(capacity);
  }

  public void set(String key, String value) {
  LRUNode node = map.get(key);
  if (node == null) {
  //判断是否超出最大长度
  if (map.size() == capacity) {
  remove(tail, true);
  }
  node = new LRUNode(key, value);
  setHead(node);
  map.put(key, node);
  return;
  }

   remove(node, false);
   node.value = value;
   setHead(node);
  

  }

  public LRUNode get(String key) {
  //map中查找
  LRUNode node = map.get(key);
  if (node == null) {
  return null;
  }
  //node 存在，将node从链表中删除，并把node放到队头
  remove(node, false);

   setHead(node);
   return node;
  

  }

  public void setHead(LRUNode node) {
  if (head == null) {
  head = node;
  tail = node;
  return;
  }

   node.next = head;
   node.prev = null;
   head = node;
  

  }

  /**

  • 移除节点

  • @param node 要移除的节点

  • @param flag 是否需要从map中删除
    */
    private void remove(LRUNode node, boolean flag) {
    if (flag) {
    map.remove(node.key);
    }

    if (node.prev == null) {//node->..
    if (node.next == null) {//node
    head = null;
    tail = null;
    } else {//node->nodeNext
    node.next.prev = null;
    head = node.next;
    }
    } else {
    if (node.next == null) {
    //head->...->node
    node.prev.next = null;
    tail = node.prev;
    } else {
    //head->..->node->...
    node.next.prev = node.prev;
    node.prev.next = node.next;
    }
    }

    node.next = null;
    node.prev = null;
    }

  @Override
  public String toString() {
  return "DoubleLink{" +
  "head=" + head.key +
  ", tail=" + tail.key +
  ", capacity=" + capacity +
  '}';
  }

  public static void main(String[] args) {
  DoubleLink cache = new DoubleLink(3);
  cache.set("1", "2");
  System.out.println(cache);

   cache.set("2", "3");
   System.out.println(cache);
   cache.set("3", "3");
   System.out.println(cache);
   cache.set("4", "3");
   System.out.println(cache);
  
  
   cache.get("3");
   System.out.println(cache);
  

  }
  }

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