设计模式--单例模式

类图

源码

package com.test;

public class StuNo {
    private static StuNo instance=null;
    private String no;
    
    private StuNo()
    {    
    }
    
    public static StuNo getInstance()
    {
        if(instance==null)
        {
            System.out.println("入学，分配学号！");
            instance=new StuNo();
            instance.setStuNo("20193922");        
        }
        else
        {
            System.out.println("返校，获取旧号码！");  
        }
        return instance;
    }
    
    private void setStuNo(String no)
    {
        this.no=no;
    }
    
    public String getStuNo()
    {
        return this.no;
    }
}


Client.java
package com.test;

public class Client {
    public static void main(String a[])
    {
        StuNo no1,no2;
       no1=StuNo.getInstance();
       no2=StuNo.getInstance();
       System.out.println("学号是否一致：" + (no1==no2));
       
       String str1,str2;
       str1=no1.getStuNo();
       str2=no1.getStuNo();
       System.out.println("第一次学号：" + str1);
       System.out.println("第二次学号：" + str2);
       System.out.println("内容是否相等：" + str1.equalsIgnoreCase(str2));
       System.out.println("是否是相同对象：" + (str1==str2));
    }
}      

测试截图