Java Community | Help. Code. Learn.•2y ago

Is there a way to return a different type in a subclass method?

I have this

public class List<E> extends java.util.ArrayList<E> {
    public List<E> add(E input) {
        super.add(input);
        return this;
    }

public class List<E> extends java.util.ArrayList<E> {
    public List<E> add(E input) {
        super.add(input);
        return this;
    }

which seems to not be valid because the method .add(E) in ArrayList returns a boolean. Is there any way I can implement this?

18 Replies

JavaBot•2y ago

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Kyo-chan•2y ago

Of course not, that would be a direct violation of polymorphism. Make a new, independant method Also you really shouldn't name your class List, since it's the name of a Java famous interface, and a superinterface of ArrayList

blockgoblin31OP•2y ago

oh it is? (damn it) thats my 3rd try to come up with a name

Kyo-chan•2y ago

What the hell does that new list do, or what the hell is that new list? Name it after that (Note that fundamentally, it's rarely smart to extend existing collections, nor even to make new ones. It happens, but it's rare)

blockgoblin31OP•2y ago

basically it fixes a couple things I found mildly annoying with ArrayList this is the last one, not being able to use .add() when defining the variable

Kyo-chan•2y ago

Are you sure that List.of() wouldn't do it?

blockgoblin31OP•2y ago

Im not familliar with that method, so probably

Kyo-chan•2y ago

List.of() produces an unmodifiable List, so it's not always the solution For some circumstances, I made my own collections builder too. But it does not extend the collections

Unknown User•2y ago

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Kyo-chan•2y ago

(yes, but it's annoying) (Also List.of() is a bit shorter than Arrays.asList())

Unknown User•2y ago

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blockgoblin31OP•2y ago

well now I feel like im complaining about nothing because the class also has(as a new method)

    public List<E> add(E[] input) {
        for (E element : input) {
            this.add(element);
        }
        return this;
    }

    public List<E> add(E[] input) {
        for (E element : input) {
            this.add(element);
        }
        return this;
    }

Unknown User•2y ago

Message Not Public

Kyo-chan•2y ago

(Actually, there is nothing convenient for a mutable ArrayList created with a non-collection set of initial values)

Unknown User•2y ago

Message Not Public

Kyo-chan•2y ago

Some variables that come from elsewhere In some cases you may even need a bunch of literal values

blockgoblin31OP•2y ago

I mostly made it a seperate class for

    public List<E> sortBy(List<E> key) {
        List<E> output = new List<>();
        for (E o : key) {
            int j = this.getCount(o);
            for (int i = 0; i < j; i++) {
                output.add(o);
            }
        }
        this.set(output);
        return output;
    }
    public void scheduleRemove(E e) {
        this.toRemove.add(e);
    }
    public void applyRemove() {
        this.remove(toRemove);
        toRemove.clear();
    }

    public List<E> sortBy(List<E> key) {
        List<E> output = new List<>();
        for (E o : key) {
            int j = this.getCount(o);
            for (int i = 0; i < j; i++) {
                output.add(o);
            }
        }
        this.set(output);
        return output;
    }
    public void scheduleRemove(E e) {
        this.toRemove.add(e);
    }
    public void applyRemove() {
        this.remove(toRemove);
        toRemove.clear();
    }

Adding that was just because it would be nice

JavaBot•2y ago

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Is there a way to return a different type in a subclass method?