Question

I’m pretty sure I can solve this problem with Java generics so I wanted to ask…Let’s say I have a few classes that each implement a common interface, there’s a method in the common interface called getData, which I’d like to make generic. The problem I have is that each class returns a different object type, so ideally I’d like these to be generic, then in the implementation class that calls getData, convert them back to their original types. If I were to cast to an Object and back to specific types I can see how that would work, but can I accomplish the same end result with Generics?

Here is some pseudo code to outline the problem:

public ClassA implements interface x {

    private CustomObjectA customObjectA;
    private Map<DateTime, Map<String, CustomObjectA>> dataMap;

...

    public Map<DateTime, Map<String, CustomObjectA>> getData() {
        return this.dataMap;
    }
}

public ClassB implements interface x {

    private CustomObjectA customObjectB;
    private Map<DateTime, Map<String, CustomObjectB>> dataMap;

...

    public Map<DateTime, Map<String, CustomObjectB>> getData() {
        return this.dataMap;
    }
}

public interface x {
    public Map<DateTime, Map<String, genericObject>> getData();
}


public ClassC {
    public testGeneric(x objX) {

        CustomObjectA cOA = objX.getData();
        CustomObjectB cOB = objX.getData();
    }
}

Answer 1

What you probably want is a generic interface :

public interface X<T> {
    Map<DateTime, Map<String, T>> getData();
}

public class A implements X<CustomObjectA> {
    @Override
    public Map<DateTime, Map<String, CustomObjectA>> getData() {
        ...
    }
}

public class B implements X<CustomObjectB> {
    @Override
    public Map<DateTime, Map<String, CustomObjectB>> getData() {
        ...
    }
}

public class C {
    public static void main(String[] args) {
        X<CustomObjectA> a = new A();
        Map<DateTime, Map<String, CustomObjectA>> m1 = a.getData();
        X<CustomObjectB> b = new B();
        Map<DateTime, Map<String, CustomObjectB>> m2 = b.getData();
    }
}