javac是否也内联? [英] Does javac also inline?

问题描述

我在玩javap和一些非常简单的代码，这引发了一个-希望是简单的-问题.

I was playing around with javap and some very simple code and that raised a - hopefully simple - question.

这是第一个代码:

public class Main {


  public static void main(String[] args) throws Exception {
    System.out.println(m1());
    System.out.println(m2());
  }

    private static String  m1() {
        return new String("foobar");
    }

    private static String m2() {
        String str = "foobar";
        return new String(str);
    }

}

现在，我编译代码并查看输出(暂时省略-verbose).

Now I compiled the code and looked at the output (omitting -verbose for now).

$ javap -c Main.class 
Compiled from "Main.java"
public class Main {
  public Main();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return        

  public static void main(java.lang.String[]) throws java.lang.Exception;
    Code:
       0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: invokestatic  #3                  // Method m1:()Ljava/lang/String;
       6: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
       9: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
      12: invokestatic  #5                  // Method m2:()Ljava/lang/String;
      15: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      18: return        
}

现在所有这些都有意义，而且我理解了不同的字节码，但是我想到的问题是:

Now all this makes sense and I understand the different byte codes, but the questions that came to my mind are:

• 我在invokestatic调用中看到了"m1"和"m2"，因此以某种方式调用了它们，但是在javap调用中却看不到它们的实际字节码输出！
• 现在，它们是内联的还是只是不显示?如果是这样，为什么?

同样，这个问题与javac在内部如何处理这些东西完全有关.谢谢！

Again this question is just of pure interest of how javac handles this stuff internally. Thanks!

推荐答案

它们在那里，但是您正在使用的默认标志不会显示它们，因为它们是私有方法.为了看到m1&的定义，平方米也要使用

They are there, but the default flags you are using doesn't show them as they are private methods. In order to see the definition for both m1 & m2 as well, use

javap -p -c .\Main.class

这将显示所有内部成员，包括私人和公共成员.如果使用上面的命令，这将是您得到的.

This will show all the internal members including private and public. This is what you will get if you use above command.

PS C:\Users\jbuddha> javap -p -c .\Main.class
Compiled from "Main.java"
public class Main {
  public Main();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return        

  public static void main(java.lang.String[]) throws java.lang.Exception;
    Code:
       0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: invokestatic  #3                  // Method m1:()Ljava/lang/String;
       6: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
       9: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
      12: invokestatic  #5                  // Method m2:()Ljava/lang/String;
      15: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      18: return        

  private static java.lang.String m1();
    Code:
       0: new           #6                  // class java/lang/String
       3: dup           
       4: ldc           #7                  // String foobar
       6: invokespecial #8                  // Method java/lang/String."<init>":(Ljava/lang/String;)V
       9: areturn       

  private static java.lang.String m2();
    Code:
       0: ldc           #7                  // String foobar
       2: astore_0      
       3: new           #6                  // class java/lang/String
       6: dup           
       7: aload_0       
       8: invokespecial #8                  // Method java/lang/String."<init>":(Ljava/lang/String;)V
      11: areturn       
}

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