Polymorphism with generics? [closed]

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I have a class A -> class B (child of A) -> class C (child of B) and class A -> class D. How can I write a function that return objects from class B and class D, example below. How to implement the calling part?

The problem is If I do A a = getFunction() I cannot access the B's functions.

public <T> T getFunction(IntegrationType integrationType) {
      return (T) integrationFactory.createIntegration(integrationType);
}

What do you mean by "class A -> class D"? Are you saying class D is a child of A? — TP95
– TP95, Commented Aug 4, 2023 at 22:50
I may not understand what you're asking, but since A is the parent, you could do something like this: A classB = new B(); A classD = new D(); classB.getFunction(): classD.getFunction(); — Jordan
– Jordan, Commented Aug 4, 2023 at 22:52
@Mahesh Have a look at java Collections class - e.g Collections.<String>emptyList() - gives you a list where the return type is List<String>.. — Mr R
– Mr R, Commented Aug 4, 2023 at 22:52
Have you tried public <T extends A> getFunction... - so then the return type is exactly what you want ... — Mr R
– Mr R, Commented Aug 4, 2023 at 22:54

Maksim Eliseev · Accepted Answer · 2023-08-04 23:18:30Z

1

The problem is If I do A a = getFunction() I cannot access the B's functions.

You can use the instanceof operator. For example:

A a = getFunction();
if (a instanceof B) {
    B b = (B) a;
    // you can call the methods of B here
}

Or, if you are using Java 16 or higher, you can try the pattern matching as follows:

A a = getFunction();
if (a instanceof B b) {
    b.someMethod();
}

answered Aug 4, 2023 at 23:18

Maksim Eliseev

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