Question

So here’s what I have:

• 1 interface called Set
• 1 abstract class which implements set
• 2 classes which extend the abstract class, called ArraySet and ListSet

So in Set, I state Iterator <String> iterator(); and then in my 2 nonabstract classes, I have nested classes which are called ArrayIterator and ListIterator, which implement the iterator’s functionality. But the compiler complains that ArraySet and ListSet must
implement Set.iterator(). How do I make it so that the compiler recognizes that ArrayIterator and ListIterator are the implementations of Set.iterator()?

So it looks like

interface Set extends Iterable< String > {  
...  
Iterator< String > iterator(); }  




class ArraySet extends AbstractClass {  
 ...  
    class ArrayIterator implements Iterator< String > { ... }  
 ...  
}  

Answer 1

You need to implement Set.iterator() in your non-abstract classes ArraySet and ListSet, ie:

In ArraySet:

Iterator<String> iterator() {
    // do something, probably return ArrayIterator ?
}

In ListSet:

Iterator<String> iterator() {
    // do something, probably return ListIterator ?
}

Also, I assume that both ArrayIterator and ListIterator implements Iterator