Question

I’m trying to make a function that takes one of many classes that extends Foo, and return a new instance of that object in its Class, not a new instance of Foo.

I’m sure this is a common issue. Is there any good examples out there?

I have never used a class as an input parameter, only members of a class. Based on what I have searched for, this should be possible to do?

Answer 1

Are you passing a Class object as the parameter, or in instance of a subclass of Foo?

The solution is almost the same in either case, you use the newInstance method on the Class object.

/**
 * Return a new subclass of the Foo class.
 */
public Foo fooFactory(Class<? extends Foo> c)
{
    Foo instance = null;
    try {
        instance = c.newInstance();
    }
    catch (InstantiationException e) {
        // ...
    }
    catch (IllegalAccessException e) {
        // ...
    }
    return instance; // which might be null if exception occurred,
                     // or you might want to throw your own exception
}

If you need constructor args you can use the Class getConstructor method and from there the Constructor newInstance(…) method.