java - 为什么 invokevirtual 的目标类型从 javac target 1.1 更改为 1.2？

Question

我知道这些是古老的 Java 版本，但我仍然很好奇。给出以下代码片段:

public void test(java.awt.event.MouseEvent e)
{
    System.out.println(e.getID());
}

当使用 javac -source 1.3 -target 1.1 编译时，会生成以下内容:

public void test(java.awt.event.MouseEvent);
 Code:
   0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
   3: aload_1       
   4: invokevirtual #3                  // Method java/awt/AWTEvent.getID:()I
   7: invokevirtual #4                  // Method java/io/PrintStream.println:(I)V
  10: return 

当使用 javac -source 1.3 -target 1.2 编译时，会生成以下内容:

public void test(java.awt.event.MouseEvent);
 Code:
   0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
   3: aload_1       
   4: invokevirtual #3                  // Method java/awt/event/MouseEvent.getID:()I
   7: invokevirtual #4                  // Method java/io/PrintStream.println:(I)V
  10: return

为什么 invokevirtual 的目标类型(参见第 4 行)从目标 1.1 更改为目标 1.2？

Answer 1

经过一些研究，似乎从 Java 1.2 开始在 javac 中引入了此更改，以便遵守 JLS 二进制兼容性规则。以下引用直接来自the javac source code :

Beginning with -target 1.2 we obey the JLS rules for binary compatibility, emitting as the qualifying type of a reference to a method or field the type of the qualifier. In earlier targets we use as the qualifying type the class in which the member was found.