设计模式 单例模式

jvm管理 线程安全的
lazy initialization holder class

内部类给单例作延时加载

public class Singleton {
    private static final class Holder {
        private static final Singleton instance = new Singleton();
    }

    private Singleton() {
    }

    public Singleton getInstance() {
        return Holder.instance;

    }
}

枚举--单例模式
enum SingletonEnum
{
  SingleObject ;  //枚举类型构造函数必须为 private 并且元素是静态的 定义完 枚举就可以使用
}


懒汉模式
public class Singleton{
    //initailzed during class loading
    private static final Singleton INSTANCE = new Singleton();
 
    //to prevent creating another instance of Singleton
    private Singleton(){}
 
    public static Singleton getSingleton(){
        return INSTANCE;
    }
}