为什么我们不应该使用==来比较字符串？ [英] Why we shouldn't use == to compare strings?

问题描述

我们可以使用显式或隐式结构创建字符串。

We can create Strings using explicit or implicit constructions.

隐式构造示例：

String str1 = "hello";
String str2 = "hello";
str1==str2 // returns true, both str1 and str2 points to the same String object in string pool

显式构造示例

String str3 = new String("hello");
String str4 = new String("hello")
str3==str4 // returns false because str3 and str4 points to different String object

由于首选（内存保存）使用隐式构造，为什么我们不应该使用==运算符？据我所知，不使用==运算符的唯一原因是我们可以忘记不使用显式结构并尝试做类似

Since it's preferred (memory save) to use implicit construction why we shouldn't use == operator? As far as I know the only one reason to not use == operator is that we can forget about not using explicit constructions and try to do something like

str1==str3
str3==str4 // and so forth

推荐答案

Literal来自您的代码的字符串被实习。这就是为什么它们在你的例子中是同一个对象。

Literal strings, coming from your code, are interned. That's why they're the same object in your example.

但是你的程序中并非所有字符串都来自你的代码，有些来自各种输入（例如用户输入）或者从文件）或者你构建它们的操作，以及那些字符串没有实现（除非你要求它）。这些字符串通常不是 == ，即使它们等于。

But not all strings in your program come from your code, some come from various inputs (for example a user input, or a file) or from operations you do to build them, and those strings aren't interned (unless you ask for it). Those strings aren't usually == even when they're equal.

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