java的equal和==问题

浏览数：17 / 时间：2015年06月08日

看一本比较简略的java教程，在看到对象的时候，书上直接给我来一句：

刚看下觉得没什么问题，很有道理的一个东东嘛，但是出于习惯还是打了几行代码测试了一下，代码如下：

 1 class Person {
 2     private String name;
 3     private int age;
 4     private double gread;
 5 
 6     public Person(String name, int age, double gread) {
 7         this.name  = name;
 8         this.age = age;
 9         this.gread = gread;
10     }
11     public String talk() {
12         return "Name: " + this.name + "\n" +
13                "Age: " + this.age + "\n" +
14                "Gread: " + this.gread;
15     }
16 }
17 
18 public class AnonymousObject {
19     public static void main(String[] args) {
20         Person per1 = new Person("wc", 21, 99);
21         Person per2 = new Person("wc", 21, 99);
22         Person per3 = new Person("wd", 21, 99);
23         System.out.println("per1 == per2: " + (per1 == per2));
24         System.out.println("per1.equals(per2): " + (per1.equals(per2)));
25         System.out.println("per1 == per3: " + (per1 == per3));
26         System.out.println("per1.equals(per3): " + (per1.equals(per3)));
27     }
28 }

预期来看，24行的结果应该是true才对，但是运行结果是：

然后我就很蛋碎的区找原因，然后发现 equals 的定义原来是这样的：

1  public boolean equals(Object obj) {
2     return (this == obj);
3     }

也就是说， equals 实质上是和 == 一样的，比较的其实都是引用，而 String 对象用 equals 比较时只要内容相同结果就为 true 的原因是 String 重写了 equals，代码如下：

 1 public boolean equals(Object anObject) {
 2     if (this == anObject) {
 3         return true;
 4     }
 5     if (anObject instanceof String) {
 6         String anotherString = (String)anObject;
 7         int n = count;
 8         if (n == anotherString.count) {
 9         char v1[] = value;
10         char v2[] = anotherString.value;
11         int i = offset;
12         int j = anotherString.offset;
13         while (n-- != 0) {
14             if (v1[i++] != v2[j++])
15             return false;
16         }
17         return true;
18         }
19     }
20     return false;
21     }