How does optimization of final references work in java?

Question

I'd been trying to figure out all about Java optimizations and found something interesting.

First case: primitive type compile-time optimization

public class Clazz {
    public static void main(String args[]) {
        final int i = 300;
        new Clazz() {
            void foo() {
                System.out.println(i);
            }
        }.foo();
    }
}

After compilation (I'm using jd-gui-0.3.5.windows to decompile binary files) it is looks like:

public class Clazz {
    public static void main(String[] args) {
        int i = 300;
        new Clazz() {
            void foo() {
                System.out.println(300);
            }
        }.foo();
    }
}

As expected, isn't it? i was replaced with it's value (inlining optimization) after compilation. So, I expected to see something similar after replacing primitive type with it's wrapper, but...

Second case: non-primitive type compile-time optimization

public class Clazz {
    public static void main(String args[]) {
        final Integer i = 300; // replaced int with Integer
        new Clazz() {
            void foo() {
                System.out.println(i);
            }
        }.foo();
    }
}

After compilation:

public class Clazz {
    public static void main(String[] args) {
        Integer i = Integer.valueOf(300);
        new Clazz() {
            void foo() {
                System.out.println(Clazz.this);
            }
        }.foo();
    }
}

Questions:

What is Clazz.this in this context? I know, that it is reference to enclosing instance of Clazz, but it should not work in that case! I need to print i, but compiler suggests me to print Clazz.this instead of it and it works! What is the problem? Does jd-gui decompiles incorrectly or do I missing something about Java compilation and optimization?

UPD:

Content of Class$1:

class Clazz$1 extends Clazz {
    Clazz$1(Integer paramInteger) {}

    void foo() {
        System.out.println(this.val$i);
    }
}

Answer 1

Does jd-gui decompiles incorrectly or do I missing something about Java compilation and optimization?

jd-gui is decompiling the code incorrectly.

On my JVM, the disassembled code for the anonymous class looks as follows:

class Clazz$1 extends Clazz {
  Clazz$1(java.lang.Integer);
    Code:
       0: aload_0       
       1: aload_1       
       2: putfield      #10                 // Field val$i:Ljava/lang/Integer;
       5: aload_0       
       6: invokespecial #12                 // Method Clazz."<init>":()V
       9: return        

  void foo();
    Code:
       0: getstatic     #20                 // Field java/lang/System.out:Ljava/io/PrintStream;
       3: aload_0       
       4: getfield      #10                 // Field val$i:Ljava/lang/Integer;
       7: invokevirtual #26                 // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
      10: return        
}

As you can see, a copy of i stored in the anonymous class, in the field called val$i (the name is implementation-specific).

It is this field that your decompiler appears to incorrectly render as Clazz.this.

Answer 2

You could simply have a look at the bytecode (javap -c Clazz$1.class).

With int i = 300:

void foo();
   0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
   3: sipush        300
   6: invokevirtual #3                  // Method java/io/PrintStream.println:(I)V
   9: return

With Integer i = 300:

void foo();
   0: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;
   3: aload_0
   4: getfield      #1                  // Field val$i:Ljava/lang/Integer;
   7: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/Object;)V
  10: return

So the int is inlined but the Integer is not.

---

Also for the record, this is what I get from jd-gui (3.0.5):

public static void main(String[] args) {
  Integer i = Integer.valueOf(300);
  new Clazz() {
    void foo() {
      System.out.println(this.val$i);
    }
  }
  .foo();
}