java/w8/Cache.java

import java.util.*;
import java.util.concurrent.locks.ReentrantReadWriteLock;


public class Cache<K, V> {
    private final Map<K, V> store;
    private final int maxCapacity;
    private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();


    public Cache(int maxCapacity) {
        if (maxCapacity <= 0) {
            throw new IllegalArgumentException("最大容量应为正数");
        }
        this.maxCapacity = maxCapacity;
        this.store = new LinkedHashMap<K, V>(16, 0.75f, true) {
            @Override
            protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
                return size() > maxCapacity;
            }
        };
    }

    public V put(K key, V value) {
        lock.writeLock().lock();
        try {
            return store.put(key, value);
        } finally {
            lock.writeLock().unlock();
        }
    }

    public V get(K key) {
        lock.readLock().lock();
        try {
            return store.get(key);
        } finally {
            lock.readLock().unlock();
        }
    }

    public V remove(K key) {
        lock.writeLock().lock();
        try {
            return store.remove(key);
        } finally {
            lock.writeLock().unlock();
        }
    }

    /**
     * 清空所有缓存。
     */
    public void clear() {
        lock.writeLock().lock();
        try {
            store.clear();
        } finally {
            lock.writeLock().unlock();
        }
    }

    /**
     * 当前缓存中的条目数。
     */
    public int size() {
        lock.readLock().lock();
        try {
            return store.size();
        } finally {
            lock.readLock().unlock();
        }
    }

    /**
     * 判断是否包含某个键。
     */
    public boolean containsKey(K key) {
        lock.readLock().lock();
        try {
            return store.containsKey(key);
        } finally {
            lock.readLock().unlock();
        }
    }

    @Override
    public String toString() {
        lock.readLock().lock();
        try {
            return store.toString();
        } finally {
            lock.readLock().unlock();
        }
    }

    // ---------- 测试示例 ----------
    public static void main(String[] args){
        Cache<String,Integer> hc1 = new Cache<String,Integer>(3);

        hc1.put("a",10);
        hc1.put("b",6);
        hc1.put("c",3);

        System.out.println("b的值为" + hc1.get("b"));
        System.out.println("a的值为" + hc1.get("a"));
        System.out.println("缓存1的条目数（键值对数）为" + hc1.size());

        hc1.remove("b");
        System.out.println("删去b后，缓存1的条目数（键值对数）为" + hc1.size());
        System.out.println("键中是否含有b：" + hc1.containsKey("b"));

        hc1.clear();
        System.out.println("清空缓存1后，缓存1的条目数（键值对数）为" + hc1.size());
    }
}