Implementations and Collections

Question

Why does this not work...

public ArrayList getEdges() {

return A;

//A is an Arraylist of type \'Action\'. Action implements Ed         


        

Answer 1

A banana is a fruit. A list of bananas is not a list of fruit.

Oherwise someone could construct a list of bananas, pass you a reference to a list of fruit, and you'd (correctly) insert an apple in it. The owner of the list of the bananas would be rightfully surprised.