Question

How can I specify that a particular parametrized type needs to have a particular method?

What I mean is: If I have my class public class SparseMatrix<type>, and one of my methods in the class (the add method) needs to use the add method of its members, how can I make it require that type has an add method? I need my SparseMatrix to be able to work with not only numbers and strings, but with other kinds of addable things too, even other matricies.

I would also be using it in my mul and sub methods.

Answer 1

You can’t just do it based on the presence of a method – the types would have to implement a common interface or superclass. For example:

public interface Addable<T>
{
    T add(T lhs, T rhs);
}

Then:

public class SparseMatrix<T extends Addable<T>>

Of course you can’t make existing types (numbers, strings) implement that interface – you’d have to write your own applicable wrapper type.