单例模式

单例模式

饿汉式，在类初始化时就创建好了单例对象

 
public class Design {

    private Design(){
        System.out.println("私有方法调用");
    }

    private static final   Design  singleton1= new Design();

    public static Design get(){
       return singleton1;
    }

   public static void jk(){
        System.out.println("kkk");
    }
}

懒汉式，只有在调用的时候才创建对象

public class Design2 {

    private Design2(){
        System.out.println("design2");
    }

    private static   Design2 singleton2 = null;
    public static Design2 getInstance(){
        if(singleton2 == null){
                 synchronized (Design2.class){
                     if(singleton2 == null){
                         singleton2 = new Design2();
                     }
                 }
        }

        return singleton2;
    }

    public static  void jk(){
        System.out.println("jk");
    }
}