java 实现LRU(最近最少使用)缓存机制

/**
 * Your LRUCache object will be instantiated and called as such:
 * LRUCache obj = new LRUCache(capacity);
 * int param_1 = obj.get(key);
 * obj.put(key,value);
 */
class LRUCache {

    Map<Integer,Integer> map ;
    Stack<Integer> stack;
    int size;
    
    public LRUCache(int capacity) {
        stack = new Stack<>();
        map = new HashMap<>(capacity);
        size = capacity;
    }
    
    public int get(int key) {
        if(!stack.contains(key)){
            return -1;
        }
        boolean flag = stack.remove(Integer.valueOf(key));
        stack.push(key);
        return map.get(key);
    }
    
    public void put(int key, int value) {
        if(stack.contains(key)){
            stack.remove(Integer.valueOf(key));
        }else{
            if(stack.size() == size){
                int count = stack.remove(0);
                map.remove(count);
            }
        }
        stack.push(key);
        map.put(key,value);
    }
}