单例之懒汉式和饿汉式

public class Singleton{ 
    private Singleton(){}
    private static Singleton singleton = null；  //不建立对象
    public static synchronized Singleton getInstance(){
             if(singleton == null) {        //先判断是否为空                
                 singleton = new Singleton ();  //懒汉式做法 
             }
             return singleton ；
     }
}

public class Singleton{ 
    public Singleton(){}
    private static Singleton singleton = new Singleton()；  //建立对象
    public static Singleton getInstance(){
        return singleton ；//直接返回单例对象    }}