java中的default equals实现如何用于String? [英] how does default equals implementation in java works for String?

问题描述

我们都知道如果我们创建两个String对象并使用==进行比较，它们将返回false，如果我们使用equals to方法将返回true.但是默认情况下，仅等于方法实现==，那么它如何返回true，它应该返回==返回的所有内容?

We all know if we create two String objects and use == to compare them it will return false and if we use equals to method it will return true. But by default equals method implement == only , then how does it return true , it should return whatever == is returning ??

推荐答案

默认情况下，是的equals方法在 Object 类中实现 == .但是，您可以在自己的类中覆盖 equals 方法，以更改在同一类的两个对象之间完成 quality 的方式.例如， String 类中的 equals 方法被覆盖如下:

Yes by default equals method implements == in Object class . But you can Override the equals method in your own class to change the way equality is done between two objects of the same class. For example the equals method in String class is overridden as follows:

public boolean equals(Object anObject) {
          if (this == anObject) {
              return true;
          }
          if (anObject instanceof String) {
              String anotherString = (String)anObject;
              int n = count;
              if (n == anotherString.count) {
                  char v1[] = value;
                  char v2[] = anotherString.value;
                  int i = offset;
                  int j = anotherString.offset;
                  while (n-- != 0) {
                      if (v1[i++] != v2[j++])
                          return false;
                  }
                  return true;
              }
          }
          return false;
      }

这就是以下代码的原因:

So this is the reason that for the following code:

String s1 = new String("java");
String s2 = new String("java");

s1 == s2 返回 false ，因为两者都在堆上引用了不同的对象.而 s1.equals(s2)返回 true ，因为现在调用的 equals 是 String 类中定义的内容，其中根据字符串的内容比较 String 对象.

s1==s2 returns false since both are referencing different objects on heap. Whereas s1.equals(s2) returns true since now the equals being called is what defined within String class where String objects are compared on the basis of contents of String.

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