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优化关于String builder和string +的对比及选择 #2444

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Expand Up @@ -683,7 +683,7 @@ System.out.println(s);

如果你使用 IDEA 的话，IDEA 自带的代码检查机制也会提示你修改代码。

不过，使用 “+” 进行字符串拼接会产生大量的临时对象的问题在 JDK9 中得到了解决。在 JDK9 当中，字符串相加 “+” 改为了用动态方法 `makeConcatWithConstants()` 来实现，而不是大量的 `StringBuilder` 了。这个改进是 JDK9 的 [JEP 280](https://openjdk.org/jeps/280) 提出的，这也意味着 JDK 9 之后，你可以放心使用“+” 进行字符串拼接了。关于这部分改进的详细介绍，推荐阅读这篇文章：还在无脑用 [StringBuilder？来重温一下字符串拼接吧](https://juejin.cn/post/7182872058743750715) 。
在 JDK 9 中，字符串相加“+”改为用动态方法 `makeConcatWithConstants()` 来实现，通过提前分配空间从而减少了部分临时对象的创建。然而这种优化主要针对简单的字符串拼接，如： `a+b+c` 。对于循环中的大量拼接操作，仍然会逐个动态分配内存（类似于两个两个 append 的概念），并不如手动使用 StringBuilder 来进行拼接效率高。这个改进是 JDK9 的 [JEP 280](https://openjdk.org/jeps/280) 提出的，关于这部分改进的详细介绍，推荐阅读这篇文章：还在无脑用 [StringBuilder？来重温一下字符串拼接吧](https://juejin.cn/post/7182872058743750715) 以及参考 [issue#2442](https://github.com/Snailclimb/JavaGuide/issues/2442)。

### String#equals() 和 Object#equals() 有何区别？

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