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

问题描述

可能重复：

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个比较s2 == s3为真？
什么是s2.toString（）返回？实际位于哪里（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 是一个无操作：

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

其次，字符串常量被实现，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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