Question

I am not very skilled in Java so I consider my question as basic. I am writing an interface for something like ArrayResult. There will be methods add and get.

Problem is that ArrayResult can obtain values of Integer or Double. So I need to define methods in interface more generally. I figured out that it is possible to have something like this for get method:

public <N extends Number> N get(Integer index);

Is that correct? I believe this means that get method can return anything what extends Number Object. What sytax to use for add method?

public void add(Number value);

This is not what I want since add(Integer value) doesnt override the interface method.

Answer 1

I guess what you want is

interface ArrayResult<N extends Number> {
    public N get(Integer index);

    public void add(N value);
}

Then you can write two separate specific implementers

class IntegerResult implements ArrayResult<Integer> {
    @Override
    public void add(Integer value) {
    }

    @Override
    public Integer get(Integer index) {
        return null;
    }
}

class DoubleResult implements ArrayResult<Double> {
    @Override
    public void add(Integer value) {
    }

    @Override
    public Double get(Double index) {
        return null;
    }
}

References:

• Bounded Type Parameters