Does using the 'this' keyword affect Java

Question

Does using the this keyword affect Java performance at all?

In this example:

class Prog {
  private int foo;

  Prog(int foo) {
    this.foo = foo;
  }
}

Is there performance overhead doing that over the following?:

class Prog {
  private int foo;

  Prog(int bar) {
    foo = bar;
  }
}

A couple of coworkers and I were discussing this earlier today and no one could come up with an answer the we all agreed on. Any definitive answer?

Answer 1

No it does not.

The code with or without this keyword after compilation is exactly the same.

Answer 2

No, not at all. It is just a different syntax for the same thing. It gets compiled into exactly the same piece of bytecode. So say it like a human: you are telling the compiler twice exactly the same thing what to do, in two different ways.

---

javap proves it. Here is with the this.:

{
  Prog(int);
    flags: 
    Code:
      stack=2, locals=2, args_size=2
         0: aload_0       
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: aload_0       
         5: iload_1       
         6: putfield      #2                  // Field foo:I
         9: return        
      LineNumberTable:
        line 4: 0
        line 5: 4
        line 6: 9
}

And here is without this.:

{
  Prog2(int);
    flags: 
    Code:
      stack=2, locals=2, args_size=2
         0: aload_0       
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: aload_0       
         5: iload_1       
         6: putfield      #2                  // Field foo:I
         9: return        
      LineNumberTable:
        line 4: 0
        line 5: 4
        line 6: 9
}

Only difference is the 2, but I had to choose a different name for the two test cases.