Special this

[Chung Huang]

It seems to me that I am running into the so call special this a lot lately.
What is the socal special this? I know that using this means the implicit reference to the object that the method is invoked on, generally. So what is the deal with the format of classname.this.something-else?

[Dan Chisholm]

That is actually called a qualified this statement. Here's an example from my mock exam.

class G {
  final String s1 = "G.s1";
  class Z {
    String s1;
    void m1() {System.out.println(???);}
  }
  public static void main(String args[]) {
    G g = new G();
    g.new Z().m1();
  }
}

What field access expression could be used in place of ??? above to cause the program to print "G.s1"? 
a.  s1 
b.  G.s1 
c.  ((G)this).s1 
d.  G.this.s1 
e.  G.super.s1 
f.  None of the Above 

The qualified this expression is used within an inner class to access a member of an enclosing class when the enclosing class member is hidden by a member of the inner class.
A similar situation exists when a member of a subclass hides a member of a super class. In that case you would just cast "this" to the type of the superclass.