懒汉式单例模式

写出懒汉式单例模式 
package www.homework.java;


class Singleton{
private static Singleton singleton;
public static Singleton getInstance(){
if(singleton==null) {
singleton= new Singleton();
}
return singleton;
}
private Singleton() {}
}


public class LazyBoy {


public static void main(String[] args) {
Singleton per=Singleton.getInstance();
Singleton per2=Singleton.getInstance();
//System.out.println(per==per2);
System.out.println(per);
System.out.println(per2);
}


}