设计模式 --单例模式

//简单的单例模式： 饿汉式： 类加载就创建对象
package Run;

class Main {
    public static void main(String[] args) {
        Single s = Single.getInstance();
        Single ss = Single.getInstance();
        System.out.println(s);
        System.out.println(ss);
    }
}

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

/*
 * 懒汉模式,类加载还没有对象
 * 延迟加载 : delay-load
 */
class Single
{
    private static Single s = null;
    
    private Single() {}
    public static Single getInstance()
    {
        if ( s == null)
            s = new Single();
        return s;
    }
}