ArrayList replace element if exists at a given index?

Question

How to replace element if exists in an ArrayList at a given index?

Answer 1

If you're going to be requiring different set functionaltiy, I'd advise extending ArrayList with your own class. This way, you won't have to define your behavior in more than one place.

// You can come up with a more appropriate name
public class SizeGenerousArrayList extends java.util.ArrayList {

    @Override
    public E set(int index, E element) {
        this.ensureCapacity(index+1); // make sure we have room to set at index
        return super.set(index,element); // now go as normal
    }

    // all other methods aren't defined, so they use ArrayList's version by default

}