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[ISSUE #2283] Add JIT article quote #2297

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Merged
Snailclimb merged 2 commits into from
Mar 3, 2024
Merged

[ISSUE #2283] Add JIT article quote #2297

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add quote article link
scwlkq Mar 2, 2024
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remove .idea
scwlkq Mar 2, 2024
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2 changes: 2 additions & 0 deletions docs/java/basis/java-basic-questions-01.md
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Expand Up @@ -88,6 +88,8 @@ JRE（Java Runtime Environment） 是 Java 运行时环境。它是运行已编

我们需要格外注意的是 `.class->机器码` 这一步。在这一步 JVM 类加载器首先加载字节码文件，然后通过解释器逐行解释执行，这种方式的执行速度会相对比较慢。而且，有些方法和代码块是经常需要被调用的(也就是所谓的热点代码)，所以后面引进了 **JIT（Just in Time Compilation）** 编译器，而 JIT 属于运行时编译。当 JIT 编译器完成第一次编译后，其会将字节码对应的机器码保存下来，下次可以直接使用。而我们知道，机器码的运行效率肯定是高于 Java 解释器的。这也解释了我们为什么经常会说 **Java 是编译与解释共存的语言** 。

> 🌈 拓展：[有关JIT的实现细节: JVM C1、C2编译器](https://mp.weixin.qq.com/s/4haTyXUmh8m-dBQaEzwDJw)

![Java程序转变为机器代码的过程](https://oss.javaguide.cn/github/javaguide/java/basis/java-code-to-machine-code-with-jit.png)

> HotSpot 采用了惰性评估(Lazy Evaluation)的做法，根据二八定律，消耗大部分系统资源的只有那一小部分的代码（热点代码），而这也就是 JIT 所需要编译的部分。JVM 会根据代码每次被执行的情况收集信息并相应地做出一些优化，因此执行的次数越多，它的速度就越快。
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