CODEWITHSUNDEEP
javagenericspolymorphism
Hackermann
Hackermann

Reputation: 43

A generic class that lets me have different return types (Java)

Today I've been working with generic/parametric types in java () exercising my polymorphism understanding but since quite some time now I've been having an issue where I would have a generic class with a single method that returns a value, the reason is because I want to be able to call a method and by context been able to have different return types

class dummy <E>{
    E value;
    public E getValue(){
         return value;
    }
class dummy1 extends dummy<E>{
    int value;
    public int getValue(){
         return int;
    }
class dummy2 extends dummy<E>{
    boolean value;
    public boolean getValue(){
         return boolean;
    }

Is this possible? I'm not really sure if even this is the correct way of doing this kind of thing

Upvotes: 2

Views: 61

Answers (1)

Tom Hawtin - tackline
Tom Hawtin - tackline

Reputation: 147164

The problem you have is that in Java primitives, such as int and boolean, cannot be generic arguments.

You need to swap these for equivalent reference types: Integer and Boolean.

Also E is scoped to the dummy class. You will need to provide the type argument to the superclass.

class Dummy<E> {
    private E value;
    public Dummy(E value) {
         this.value = value;
    }
    public E getValue() {
         return value;
    }
}
class Dummy1 extends Dummy<Integer> {
    public Dummy1(Integer value) {
         this.value = value;
    }
}
class Dummy2 extends Dummy<E> {
    public Dummy2(Boolean value) {
         this.value = value;
    }
}

Or:

abstract class Dummy<E> {
    public abstract E getValue();
}
class ReferenceDummy<E> extends Dummy<E> {
    private final E value;
    public Dummy1(E value) {
         this.value = value;
    }
    @Override public E getValue() {
         return value;
    }
}
class Dummy1 extends Dummy<Integer> {
    private int value;
    public Dummy1(int value) {
         this.value = value;
    }
    @Override public Integer getValue() {
         return value;
    }
}
class Dummy2 extends Dummy<Boolean> {
    private boolean value;
    public Dummy1(boolean value) {
         this.value = value;
    }
    @Override public Boolean getValue() {
         return value;
    }
}

Note that, say, boolean getValue() cannot override Boolean getValue() for some reason.

Upvotes: 5

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