Java编译器会预先计算文字和吗? [英] Will the Java compiler precalculate sums of literals?

问题描述

int i = 10 + 20;

编译器将添加10 + 20来处理该代码，这是真的吗?字节代码是否与该行代码相同?

Is it true that the compiler will process this code, adding 10 + 20, and the byte code is the same as for this line of code?

int i = 30;

我在哪里可以读到它?

推荐答案

是的，您甚至可以自己进行验证.以一个小的Java文件为例:

Yes, and you can even verify it for yourself. Take a small Java file, for example:

public class Main {
  public Main() {
    int i = 10 + 20;
  }
}

使用javac Main.java进行编译，然后运行javap -c Main进行反汇编:

Compile it with javac Main.java, and then run javap -c Main to disassemble it:

Compiled from "Main.java"
public class Main extends java.lang.Object{
public Main();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   bipush  30
   6:   istore_1
   7:   return

}

很明显，在字节码中，您可以看到编译器的优化:bipush 30！

Clearly in the bytecode, you can see the compiler's optimization: bipush 30!

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