LRU 内存淘汰策略

系列文章目录

一、LRU-Least recently used

是一种常用的内存淘汰策略，用于在缓存满时删除最近最少使用的数据，核心思想：当缓存空间不足，移除最久未被访问的数据

package com.citi.leetcode;import java.util.LinkedHashMap;public class LRU<K,V> extends LinkedHashMap<K, V> {private final int capacity;public LRU(int capacity) {//true for access order//第三个参数是 accessOrder，设为 true 表示按照访问顺序排序，而不是插入顺序。
//removeEldestEntry() 是 LinkedHashMap 提供的方法，返回 true 时会移除最老的条目（即最近最少使用的）。super(capacity, 0.75f, true);this.capacity = capacity;}@Overrideprotected boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {return size() > capacity;//当缓存空间超过capacity时，返回true，删除最老的节点}public static void main(String[] args) {LRU<Integer, String> cache = new LRU<>(3);cache.put(1, "A");cache.put(2, "B");cache.put(3, "C");System.out.println("After inserting 1,2,3:"+cache);cache.get(1);//访问1，变成最近使用cache.put(4, "D");//插入4，容量已满，移除最久未使用的2System.out.println("After accessing 1 and inserting 4:"+cache);}
}

二、自定义LRU

package com.citi.leetcode;import java.util.HashMap;
import java.util.Map;class LRUCacheManual<K, V> {private final int capacity;private final Map<K, Node> map;private Node head, tail;static class Node<K, V> {K key;V value;Node prev, next;public Node(K key, V value) {this.key = key;this.value = value;}}public LRUCacheManual(int capacity) {this.capacity = capacity;this.map = new HashMap<>();}public V get(K key) {if (!map.containsKey(key)) {return null;}Node node = map.get(key);moveToHead(node);return (V) node.value;}public void put(K key, V value) {if (map.containsKey(key)) {Node node = map.get(key);node.value = value;moveToHead(node);} else {Node newNode = new Node<>(key, value);map.put(key, newNode);addNode(newNode);if (map.size() > capacity) {Node last = tail;map.remove(last.key);removeNode(last);}}}private void addNode(Node node) {node.prev = null;node.next = head;if (head != null) {head.prev = node;}head = node;if (tail == null) {tail = node;}}private void removeNode(Node node) {if (node.prev != null) {node.prev.next = node.next;} else {head = node.next;}if (node.next != null) {node.next.prev = node.prev;} else {tail = node.prev;}}private void moveToHead(Node node) {removeNode(node);addNode(node);}public static void main(String[] args) {LRUCacheManual<Integer, String> cache = new LRUCacheManual<>(3);cache.put(1, "One");cache.put(2, "Two");cache.put(3, "Three");System.out.println(cache.get(1)); // Onecache.put(4, "Four"); // 移除 2System.out.println(cache.get(2)); // nullSystem.out.println(cache.get(1)); // One}
}