基于LinkedHashMap的LRU缓存实现（FIFO亦可）

怼烎@ 2023-10-05 17:18 21阅读 0赞

import java.util.LinkedHashMap;
    import java.util.Map;
    import java.util.Set;
    
    /**
     * @author wh445306
     * @version 1.0
     * @Desciption:LRUCache 参考：https://www.cnblogs.com/lzrabbit/p/3734850.html
     * @date 2021-01-06 18:06
     */
    
    public class LRUCache <K, V>{
        private final int MAX_CACHE_SIZE;
        private final float DEFAULT_LOAD_FACTORY = 0.75f; 
    
        LinkedHashMap<K, V> map;
    
        public LRUCache(int cacheSize) {
            MAX_CACHE_SIZE = cacheSize;
            int capacity = (int)Math.ceil(MAX_CACHE_SIZE / DEFAULT_LOAD_FACTORY) + 1;
            /*
             * HashMap负载因子默认即为0.75，是一个折衷的取值
             * 第三个参数设置为true，代表linkedlist按访问顺序排序，可作为LRU缓存
             * 第三个参数设置为false，代表按插入顺序排序，可作为FIFO缓存
             */
            map = new LinkedHashMap<K, V>(capacity, DEFAULT_LOAD_FACTORY, true) {
                @Override
                protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
                    return size() > MAX_CACHE_SIZE;
                }
            };
        }
    
        public synchronized void put(K key, V value) {
            map.put(key, value);
        }
    
        public synchronized V get(K key) {
            return map.get(key);
        }
    
        public synchronized void remove(K key) {
            map.remove(key);
        }
    
        public synchronized Set<Map.Entry<K, V>> getAll() {
            return map.entrySet();
        }
    
        public synchronized int size() {
            return map.size();
        }
    
        public synchronized void clear() {
            map.clear();
        }
    
        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();
            for (Map.Entry<K, V> entry : map.entrySet()) {
                sb.append(String.format("%s: %s  ", entry.getKey(), entry.getValue()));
            }
            return sb.toString();
        }
    
        //测试
        public static void main(String[] args) {
            LRUCache<Integer, Integer> lru = new LRUCache<>(5);
            lru.put(1, 1);
            lru.put(2, 2);
            lru.put(3, 3);
            System.out.println(lru);
            lru.get(1);
            System.out.println(lru);
            lru.put(4, 4);
            lru.put(5, 5);
            lru.put(6, 6);
            System.out.println(lru);
        }
    }

效果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3doNDQ1MzA2_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3doNDQ1MzA2_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20210106225442993.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3doNDQ1MzA2,size_16,color_FFFFFF,t_70