Overloading with interfaces as parameters

Question

Let's say you have two interfaces If1 and If2. Consider the following class:
public class FooBar{
  public void doIt(If1 i){
    //Do Something
  public void doIt(If2 i){
    //Do Something
}My instinct tells me that this shouldn't compile--after all, you can have a class that implements both If1 and If2, and then Java won't know which one to call. But it does compile. How does Java figure out which method to call in the case of a class that implements If1 and If2?

Answer 1

My instinct tells me that this shouldn't compile--after all, you can have a class that implements both If1 and If2, and then Java won't know which one to call.The java compiler will worry about how an object of that class is declared:
public class FooBar {
    public void doIt(If1 i){
        System.out.println("1");
    public void doIt(If2 i){
        System.out.println("2");
    public static void main(String[] args) {
        If2 arg = new X();
        new FooBar().doIt(arg);
        X badarg = new X();
        new FooBar().doIt(badarg);
interface If1 {}
interface If2 {}
class X implements If1, If2 {}The second doIt() invocation upsets the compiler because it really is ambiguous.
You might wan to consider variations like "If2 extends If1" and see if you can predict the compiler and runtime's behaviour. Details in the JLS.
Edited by: pbrockway2 on Jun 24, 2008 12:58 PM