单例设计模式（饿汉式，懒汉式）

 1 package com.yhqtv.test;
 2 //饿汉式
 3 public class SingletonTest1 {
 4     public static void main(String[] args) {
 5         Bank bank1 = Bank.getIntstance();
 6         Bank bank2 = Bank.getIntstance();
 7 
 8         System.out.println(bank1==bank2);
 9     }
10 
11 }
12  class Bank{
13 
14     //1.私有化的构造器
15     private Bank(){
16 
17     }
18 
19     //2、内部创建类的对象
20     //4.要求此对象也必须声明为静态
21      private static Bank intstance=new Bank();
22 
23     //3.提供公共的静态的方法，返回类的对象
24      public static Bank getIntstance(){
25          return intstance;
26      }
27 
28 }

 1 package com.yhqtv.test;
 2 //懒汉式
 3 public class SingletonTest2 {
 4     public static void main(String[] args) {
 5         Order order1=Order.getInstance();
 6         Order order2=Order.getInstance();
 7 
 8         System.out.println(order1==order2);
 9 
10     }
11 
12 }
13 class Order{
14 
15     //1.私有化的构造器
16     private Order(){
17 
18     }
19 
20     //2、s声明当前类对象，没有初始化
21     //4.此对象也必须声明static
22     private static Order instance=null;
23 
24     //3.声明public、static的返回当前类的对象方法
25     public static Order getInstance(){
26         if(instance==null){
27             instance=new Order();
28 
29         }
30         return instance;
31     }
32 }