单例模式

1.饿汉模式

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

2.懒汉模式

class Single{
    private static Single instance =null;
    private Single(){}
    private static Single getInstance(){
        if(instance==null){
            instance=new Single();
        }
        return instance;
    }
}