能使用的单例代码

public class Singleton {private Singleton(){};private static class SingletonHolder{private static Singleton singleton=new Singleton();}public static Singleton getInstance(){return SingletonHolder.singleton;}public static void main(String[] args) {Singleton2.Singleton.sys();}}enum Singleton2{Singleton("test");private String param;private Singleton2(String param){this.param=param;}public void sys(){System.out.println(param);}}