最终的静态变量操作，编译还是运行时？ [英] Final static variables operations, compile or runtime?

问题描述

最终的静态变量操作是在运行时还是编译时发生的？例如：

Do final static variables operations happen in run-time or compile time ? For example:

public static final int ID_1 = 1;
public static final int ID_2 = 2;

public static int test(){
    return ID_1 + ID_2; // Does this addition execute in compile or runtime ?
}

推荐答案

这里有一个提示： https://docs.oracle.com/javase/tutorial/java/javaOO /classvars.html

它说：

如果是原始类型或字符串被定义为常量，并且该值在编译时是已知的，编译器将代码中的常量名称替换为其值。

If a primitive type or a string is defined as a constant and the value is known at compile time, the compiler replaces the constant name everywhere in the code with its value.

因此，一旦完成并且您在方法中以 1 + 2 结束，那么优化它也是合乎逻辑的并且只是使用 3 在编译时。

So once that is done and you end up with 1 + 2 in the method, it would be logical for that to be optimized as well and just use the 3 at compile time.

为了在实践中证明它，你可以编译你的代码，然后将其反编译为看看发生了什么。

To prove it in practice, you can compile your code and then decompile it to see what's going on.

我尝试使用JD-GUI，这是我在反编译代码时得到的结果：

I tried with JD-GUI and this is what I got when decompiling your code:

    public class TestCompileOrRuntime
    {
      public static final int ID_1 = 1;
      public static final int ID_2 = 2;

      public static int test()
      {
        return 3;
      }
    }

所以看起来在这种情况下编译器正在解决在编译时运行。

So it looks in this case the compiler is solving the operation in compile time.

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