lamby

Java Quiz

public class Overload {
    public static void main(String args[]) {
        int result = foo(new B(), new B());
        System.out.println(result);
    }

    public static int foo(A a, B b) { return 1; }
    public static int foo(B b, A a) throws Exception { return 2; }

    static class A { }
    static class B extends A { }
}

Without using a compiler (using the JLS and JLS report is allowed), answer the following:

1. Does this code compile?
2. If yes - what is the result from running the program?
3. If no - why not? List all errors.

Answers on a postcard.

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Four comments

1. No. The compiler will be unable to work out unique signatures (or whatever they're called) for the methods.

   mChicago

2. Mmm, correct. The "throws Exception" was just to confuse people - although the defined exception sometimes feels like part of the signature.

   So the code is incorrect because of the presence of "override-equivalent signatures." (See
   http://java.... for a more formal treatment)

   — lamby

3. Sorry, I am struggling to work out where an exception would be considered to be part of the signature - that would suggest that the following two would be a "good" compile:
   <code>
   private int foo ( int a ) { return 1; }
   private int foo ( int a ) throws Exception { return 1; }</code>

   Unfortunatly, Ive found a problem in C#, which is legal in terms of the language, but obviously bad:
   <code>
   class foo {
   public int bar(){
   return 1;
   }
   public static int bar() {
   return 2;
   }
   }</code>

   In this instance, when coding inside a function in the class, static and non-static functions can both be referenced without a this. However, in this case, it is unclear which one actually would run:
   <code>
   this.bar() == 1;
   foo.bar() == 2;
   bar() -> ?</code>

   What is interesting, is that the compiler treats the two sets of results differently, and therefore the signatures do not need to be similar. The static could return a string, and the non-static an int.

   Fun.

   mChicago

4. code will not complie

   manish

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