class Foo {}

public class Test {
        public Foo makeFoo(String p,String q) {
                return new Foo(){
                        public void doSomething() {
                                System.out.println(p);
                        }
                };
        }
}

当你编译并运行javap -c -p’Test $1.class’时,你得到这个：

Compiled from "Test.java"
class Test$1 extends Foo {
  final java.lang.String val$p;

  final Test this$0;

  Test$1(Test,java.lang.String);
    Code:
       0: aload_0
       1: aload_1
       2: putfield      #1                  // Field this$0:LTest;
       5: aload_0
       6: aload_2
       7: putfield      #2                  // Field val$p:Ljava/lang/String;
      10: aload_0
      11: invokespecial #3                  // Method Foo."<init>":()V
      14: return

  public void doSomething();
    Code:
       0: getstatic     #4                  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: aload_0
       4: getfield      #2                  // Field val$p:Ljava/lang/String;
       7: invokevirtual #5                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      10: return
}

当创建匿名类时,变量p被捕获到val $p中(如预期的那样,因为它是必需的),而变量q不是(正如预期的那样,因为它不需要).但是,Test.this被捕获到这个$0,即使它不需要.这是Java规范的强制要求,还是它恰好的工作方式？为什么这样工作？