The size of the board is one of the differences between elevens and thirteens. why is size not an abstract method?

The program keeps track of the size of the board in cards.size(). The sub class sets this by passing it into the constructor. After that, the subclass never cares about the size of the board, so it's not necessary to make it accessible with an abstract method. Any need for it is covered by cardIndexes method.

Explanation:

The differences between Elevens and Thirteens

The program keeps track of the size of the board in cards.size(). The sub class sets this by passing it into the constructor. After that, the subclass never cares about the size of the board, so it's not necessary to make it accessible with an abstract method. Any need for it is covered by cardIndexes method.