How to use generics in Java to return numbers?

I have a class similar to the following, but I have a question about using generic return values

import java.util.ArrayList;
public class @R_724_2419@<T extends Number> {
    private ArrayList<T> list;
    public @R_724_2419@(){
        list = new ArrayList<T>();
    }
    public T get(int i){
        if(i <list.size())
            return list.get(i);
        else
            return 0; // Problem
    }
}

When I < 1, I must get 0 (or 0.0 - depending on the value of T) list Size () cannot be empty How to code this correctly?

Solution

If you really want to return 0 by default, you can do this:

public abstract class @R_724_2419@<T extends Number> {
    private List<T> list;

     public @R_724_2419@(){
        list = new ArrayList<T>();
    }

    public T get(int i){
        if(i <list.size())
            return list.get(i);
        else
            return getDefault();
    }

    protected abstract T getDefault();
}

Then there is an implementation for each number subclass you want to support, such as

public class Integer@R_724_2419@ extends @R_724_2419@<Integer> {

    @Override
    protected Integer getDefault() {
        return 0;
    }
}

and

public class Double@R_724_2419@ extends @R_724_2419@<Double> {

    @Override
    protected Double getDefault() {
        return 0D;
    }
}

wait

A good feature is that it can return any default value, not just zero... And the same principle does not work for any type of object, not just numbers