LRU实现

使用LinkedHashMap,特性是插入有序
重写removeEldestEntry(Map.Entry eldest)方法

/**
     * Returns true if this map should remove its eldest entry.
     * This method is invoked by put and putAll after
     * inserting a new entry into the map.  It provides the implementor
     * with the opportunity to remove the eldest entry each time a new one
     * is added.  This is useful if the map represents a cache: it allows
     * the map to reduce memory consumption by deleting stale entries.
     *
     * 
Sample use: this override will allow the map to grow up to 100
     * entries and then delete the eldest entry each time a new entry is
     * added, maintaining a steady state of 100 entries.
     * 
     *     private static final int MAX_ENTRIES = 100;
     *
     *     protected boolean removeEldestEntry(Map.Entry eldest) {
     *        return size() > MAX_ENTRIES;
     *     }
     * 
     */

代码

import java.util.LinkedHashMap;
import java.util.Map;

public class LRUCache<K, V> extends LinkedHashMap<K, V> {
    private int cacheSize;

    public LRUCache(int cacheSize) {
        super(16, 0.75f, true);
        this.cacheSize = cacheSize;
    }

    @Override
    protected boolean removeEldestEntry(Map.Entry eldest) {
        return size() > cacheSize;
    }
}