Question

Okay, so I’m making a dynamic 2D array in Java that implements the java.util.Collection interface. I made my array implement it because I wanted it to have the same functionality as a normal Collection. However, I cannot implement the size() method because in the interface it returns an integer and a 2D matrix could potentially overflow an integer type.

Here’s a snippet of my class I’m trying to make:

public abstract class AbstractMatrix<E> implements Collection<E>{
     @Override
     public long size() {
         return columns * rows;
     }
}

Now, this won’t work because “The return type is incompatible with Collection<E>.size()“, and if I change the type to int, columns * rows could overflow.

I know I can’t override the size method like this, but is there any way I can make sure the method returns the correct size while still implementing the Collection interface?

Yes, I know this is impractical and will likely never be an issue, but I was interested to know if there was a good solution for it.

Answer 1

Although your implementation of size is questionable, the contract for Collection#size is defined in the javadoc:

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

So you could calculate the size as a long, and return Integer.MAX_VALUE if it is larger than Integer.MAX_VALUE.

Alternatively, you could mimic the way it is implemented in LinkedList#add for example, where size is simply incremented and is allowed to overflow.