多线程高并发单例模式

内部类实例化static inner class

/**
 * 静态内部类做单例
 *
 */
public class Singletion {

private static class InnerSingletion {
private static Singletion single = new Singletion();
    }

public static Singletion getInstance(){
return InnerSingletion.single;
    }

}

2次检查实例化dubble check instance

public class DubbleSingleton {

private static DubbleSingleton ds;

public  static DubbleSingleton getDs(){
if(ds == null){
//【等待位置】
            synchronized (DubbleSingleton.class) {
if(ds == null){
//初始化有可能耗时比较长，导致N个线程到达【等待位置】，如果这里不第二次检查ds，就会生成N个新实例对象。
                    ds = new DubbleSingleton();
                }
            }
        }
return ds;
    }
}