Java 中的字符串:equals vs == [英] Strings in Java : equals vs ==

问题描述

可能的重复:
如何比较 Java 中的字符串?

  String s1 = "andrei";
  String s2 = "andrei";

  String s3 = s2.toString();

  System.out.println((s1==s2) + " " + (s2==s3));

给出以下代码为什么第二次比较 s2 == s3 为真?s2.toString() 返回的是什么?实际位置在哪里 (s2.toString()) ?

Giving the following code why is the second comparison s2 == s3 true ? What is actually s2.toString() returning ? Where is actually located (s2.toString()) ?

推荐答案

首先 String.toString 是一个空操作:

First of all String.toString is a no-op:

/**
 * This object (which is already a string!) is itself returned.
 *
 * @return  the string itself.
 */
public String toString() {
    return this;
}

其次，String 常量是 interned，因此 s1 和 s2 在幕后更改为相同的 String 实例.

Second of all, String constants are interned so s1 and s2 are behind the scenes changed to be the same String instance.

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