A question from a beginner

Question

I'm teaching a introductory programming course in java to some folks, and explaining variable lifetimes and the need for object member variables to store values longer than just a method call.
So the example given was of a parameter being saved in a member variable
The question arose, "Why can't you just specify the member variable as the parameter?"
To which i gave the obvious reasons.
When the class was over, i thought about it some more, and except for syntactic unpleasantries, there is no reason why this couldn't be done. Given that this is a common idiom, its odd that you can't do that.
It's only not odd, because it's never been done before.
Just thought it was an interesting thought that new-person thought produced.

Answer 1

To paraphrase the JLS: When the method or constructor is invoked, the values of the actual argument expressions initialize newly created parameter variables, each of the declared type, before execution of the body of the method or constructor. The identifier may be used as a simple name in the body of the method or constructor to refer to the formal parameter. Taking your example:
public class Foo {
  private int input;
  public void setInput( int Foo.input ) {}
}Here you are not initializing any newly created parameter variables, and you have no identifier that may be used as a simple name in the body of the method or constructor to refer to the formal parameter. This breaks another part of the language specification which states that formal parameters are referred to only using simple names, never by using qualified names. You might also get into issues with the float-extended-exponent value set and the double-extended-exponent value set.
Alternatively, you may just be suggesting that the compiler perform qualified name erasure to transform:
public class Foo {
  private int input;
  public void setInput( int Foo.input ) {}
}to:
public class Foo {
  private int input;
  public void setInput( int input ) {
    this.input = input;
}If this is the case, isn't syntactic sugar supposed to makes things "sweeter" to use? IMHO, this syntax isn't.