Introduction to Java lesson 91 -- overriding the equals method of the cell class

Monkeys learn to program 2020-11-13 02:42:16
introduction java lesson overriding equals


problem

    Java There are two ways to test whether two variables are equal in a program : One is to make use of == Operator , The other is to use equals.

     When using == When comparing two reference variables , They must point to the same object ,== Judgment will return true.

    equals The method is Object Class provides an instance method , Therefore, all reference variables can call this method to determine whether they are equal to other reference variables . But use this method to judge the equality of two objects == There is no difference between operators , It also requires two reference variables to point to the same object to return true. So the Object Class provides the equals The method doesn't have much practical significance , If you want to use a custom equivalent , You can use rewrite equals Method .

     This case requires that Cell Class equals Method , Two Cell The condition of reference variable equality is row row equality , Column column equality .

programme

     First , On the basis of the previous case , stay Cell Class equals Method , Two Cell The condition of reference variable equality is row row equality , Column column equality

     then , test equals Whether the method override works . First , In the class TestCell Add test method to testEquals, then , establish cell1 Objects and cell2 object , The code is as follows :

Cell cell1=new Cell(6,3);
Cell cell2=new Cell(6,3);

     Finally, we use == and equals Compare cell1 Objects and cell2 Whether objects are equal .

step

     To implement this case, follow the steps below .

Step one : stay Cell Class equals Method

     On the basis of the previous case , stay Cell Class equals Method , Two Cell Reference variable call equals Method returns ture The condition is that the rows are equal , Column column equality , The code is as follows :

 package day02;
    
    public class Cell{
        int row;
        int col;
        
        public Cell(int row,int col){
            this.row=row;
            this.col=col;
        }
        
        public Cell(){
            this(0,0);
        }
        
        public Cell(Cell cell){
            this(cell.row,cell.col);
        }
        
        public void drop(){
            row++;
        }
        
        public void moveRight(){
            col++;
        }
        
        public void moveLeft(){
            col--;
        }
        
        @Override
        public String toString(){
            return row+","+col;
        }
        
        @Override
        public boolean equals(Object obj){
            if(obj==null){
                return false;
            }
            if(this==obj){
                return true;
            }
            if(obj instanceof Cell){
                Cell cell=(Cell)obj;
                return cell.row==row&&cell.col==col;
            }else{
                return false;
            }
        }
    }

Step two : test equals Whether the method works

     test equals Whether the method override works . First , In the class TestCell Add test method to testEquals, then , establish cell1 Objects and cell2 object ; Finally, we use == and equals Compare cell1 Objects and cell2 Whether objects are equal , The code is as follows :

 package day02;
    
    import org.junit.Test;
    
    public class TestCell{
    
    /**
     * test equals Method
     */
     @Test
     public void testEquals(){
         Cell cell1=new Cell(6,3);
         Cell cell2=new Cell(6,3);
         System.out.println(cell1==cell2);//false
         System.out.println(cell1.equals(cell2));//true
     }
    }

Step three : function

     function testEquals Method , The console output is as follows :

    false
    true

     As you can see from the results , Use == The result of the comparison is false、 Use equals The result of the comparison is true, explain Cell Class successfully covered equals Method , It realizes the equality of rows and columns Cell The reference variables of are equal .

Official account , Get a learning video

版权声明
本文为[Monkeys learn to program]所创,转载请带上原文链接,感谢

  1. [front end -- JavaScript] knowledge point (IV) -- memory leakage in the project (I)
  2. This mechanism in JS
  3. Vue 3.0 source code learning 1 --- rendering process of components
  4. Learning the realization of canvas and simple drawing
  5. gin里获取http请求过来的参数
  6. vue3的新特性
  7. Get the parameters from HTTP request in gin
  8. New features of vue3
  9. vue-cli 引入腾讯地图(最新 api,rocketmq原理面试
  10. Vue 学习笔记(3,免费Java高级工程师学习资源
  11. Vue 学习笔记(2,Java编程视频教程
  12. Vue cli introduces Tencent maps (the latest API, rocketmq)
  13. Vue learning notes (3, free Java senior engineer learning resources)
  14. Vue learning notes (2, Java programming video tutorial)
  15. 【Vue】—props属性
  16. 【Vue】—创建组件
  17. [Vue] - props attribute
  18. [Vue] - create component
  19. 浅谈vue响应式原理及发布订阅模式和观察者模式
  20. On Vue responsive principle, publish subscribe mode and observer mode
  21. 浅谈vue响应式原理及发布订阅模式和观察者模式
  22. On Vue responsive principle, publish subscribe mode and observer mode
  23. Xiaobai can understand it. It only takes 4 steps to solve the problem of Vue keep alive cache component
  24. Publish, subscribe and observer of design patterns
  25. Summary of common content added in ES6 + (II)
  26. No.8 Vue element admin learning (III) vuex learning and login method analysis
  27. Write a mini webpack project construction tool
  28. Shopping cart (front-end static page preparation)
  29. Introduction to the fluent platform
  30. Webpack5 cache
  31. The difference between drop-down box select option and datalist
  32. CSS review (III)
  33. Node.js学习笔记【七】
  34. Node.js learning notes [VII]
  35. Vue Router根据后台数据加载不同的组件(思考->实现->不止于实现)
  36. Vue router loads different components according to background data (thinking - & gt; Implementation - & gt; (more than implementation)
  37. 【JQuery框架,Java编程教程视频下载
  38. [jQuery framework, Java programming tutorial video download
  39. Vue Router根据后台数据加载不同的组件(思考->实现->不止于实现)
  40. Vue router loads different components according to background data (thinking - & gt; Implementation - & gt; (more than implementation)
  41. 【Vue,阿里P8大佬亲自教你
  42. 【Vue基础知识总结 5,字节跳动算法工程师面试经验
  43. [Vue, Ali P8 teaches you personally
  44. [Vue basic knowledge summary 5. Interview experience of byte beating Algorithm Engineer
  45. 【问题记录】- 谷歌浏览器 Html生成PDF
  46. [problem record] - PDF generated by Google browser HTML
  47. 【问题记录】- 谷歌浏览器 Html生成PDF
  48. [problem record] - PDF generated by Google browser HTML
  49. 【JavaScript】查漏补缺 —数组中reduce()方法
  50. [JavaScript] leak checking and defect filling - reduce() method in array
  51. 【重识 HTML (3),350道Java面试真题分享
  52. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  53. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  54. [re recognize HTML (3) and share 350 real Java interview questions
  55. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  56. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  57. 【重识 HTML ,nginx面试题阿里
  58. 【重识 HTML (4),ELK原来这么简单
  59. [re recognize HTML, nginx interview questions]
  60. [re recognize HTML (4). Elk is so simple