对象池模式（Object Pool Pattern）

public class Client {
    public static void main(String[] args) {        ObjectPool pool = new ObjectPool(10,50);        IPooledObject object = pool.borrowObject();        object.operation();        pool.returnObject(object);        System.out.println();    }
    //抽象对象    interface IPooledObject {        void operation();    }    //具体对象    static class ConcretePoolObject implements IPooledObject {        public void operation() {            System.out.println("doing");        }    }
    //对象池    static class ObjectPool {        private int step = 10;            //当对象不够用的时候，每次扩容的数量        private int minCount;        private int maxCount;        private Vector<IPooledObject> returneds;   //保存未借出的对象        private Vector<IPooledObject> borroweds;   //保存已被借出的对象
        //初始化对象池        public ObjectPool(int minCount,int maxCount){            borroweds = new Vector<IPooledObject>();            returneds = new Vector<IPooledObject>();
            this.minCount = minCount;            this.maxCount = maxCount;
            refresh(this.minCount);        }
        //因为内部状态具备不变性，所以作为缓存的键        public IPooledObject borrowObject() {            IPooledObject next = null;            if(returneds.size() > 0){                Iterator<IPooledObject> i = returneds.iterator();                while (i.hasNext()){                    next = i.next();                    returneds.remove(next);                    borroweds.add(next);                    return next;                }            }else{                //计算出剩余可创建的对象数                int count = (maxCount - minCount);                //剩余可创建的数量大于单次固定创建的对象数                //则再初始化一批固定数量的对象                refresh(count > step ? step : count);            }            return next;        }
        //不需要使用的对象归还重复利用        public void returnObject(IPooledObject pooledObject){            returneds.add(pooledObject);            if(borroweds.contains(pooledObject)){                borroweds.remove(pooledObject);            }        }
        private void refresh(int count){            for (int i = 0; i < count; i++) {                returneds.add(new ConcretePoolObject());            }        }    }}