设计模式04：单例模式

单例模式，比较简单。UML如下

饿汉式：

public class Single {
    private static Single single=new Single();
    private Single(){}
    public static Single getInstance(){
        return single;
    }
}

懒汉式：方法体上需要加synchronized关键字

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