Where is stored captured variable in Java?

Question

I\'m trying to understand concept of captured variable in Java.

I found quite detailed article about it: http://www.devcodenote.com/2015/04/variable-capture-in-java.html

Answer 1

The author seems to be referring to the fact that captured variables are translated into fields of a local/anonymous class.

If you disasemble LocalClass you can see this (where Main is the name of the enclosing class):

class Main$1LocalClass {
  final int val$y;

  final Main this$0;

  Main$1LocalClass();
    Code:
       0: aload_0
       1: aload_1
       2: putfield      #1                  // Field this$0:LMain;
       5: aload_0
       6: iload_2
       7: putfield      #2                  // Field val$y:I
      10: aload_0
      11: invokespecial #3                  // Method java/lang/Object."<init>":()V
      14: getstatic     #4                  // Field java/lang/System.out:Ljava/io/PrintStream;
      17: aload_0
      18: getfield      #2                  // Field val$y:I
      21: invokevirtual #5                  // Method java/io/PrintStream.println:(I)V
      24: return
}

The first field is the local variable y, and the second field is a reference to the enclosing instance. Furthermore, these values are passed into the constructor of the local class implicitly.

Essentially LocalClass looks like this:

class LocalClass {
    final int val$y;
    final Main this$0;

    LocalClass(Main arg1, int arg2) {
        this.this$0 = arg1; // bytecode 1-2
        this.val$y = arg2; // bytecode 5-7
        super(); // bytecode 10-11
        System.out.println(this.val$y); // bytecode 14-21
    }
}