Question

This is my overall workflow. First create an interface:

public interface foo {
   void bar(Baz b);
}

Then make, for example, a vector with different objects that all implement said interface:

myVector.add(new Ex);  //both Ex and Why implement foo.
myVector.add(new Why); 

And finally, use the interface:

for(int i=0; i<myVector.size(); i++) {
    myVector.get(i).bar(b);
}

However, for obvious reasons, this produces a compile time error:

The method bar() is undefined for the type Object

Casting won’t work because Ex and Why aren’t related. Try-catch casting to Ex and then Why is a horrible work-around. Making both Ex and Why extend Bar_doers also doesn’t sound succinct either, as that would be doing away with interfaces.

How can I perform operations that care about whether an Object implements a given interface, not whether an object is of a given class?

Answer 1

You need to read about generics.

Assuming you were using a standard Java container, then the solution in your case is to define myVector thus:

List<foo> myVector = new ArrayList<foo>();