无加锁创建单例

public class StaticSingleton {
    private StaticSingleton(){
        System.out.println("StaticSingleton is created");
    }
    private static class SingletonHolder{
        private static StaticSingleton instance=new StaticSingleton();
    }
    public static StaticSingleton getInstance(){
        return SingletonHolder.instance;
    }
}