Implement the Iterator Pattern

Part I

We are going to implement our iterator for ArrayIndexedList (instead of using the Arrays.stream(data).iterator).

• Add a new class ArrayIndexedListIterator:

  public class ArrayIndexedListIterator<T> {
  
  } 
  

• ArrayIndexedListIterator must implement the Iterator interface:

  public class ArrayIndexedListIterator<T> implements Iterator<T> {
  
  } 
  

• The following operations from the Iterator interface are inherited (and need to be implemented):

  public class ArrayIndexedListIterator<T> implements Iterator<T> {
  
    @Override
    public boolean hasNext() {
      return false;
    }
  
    @Override
    public T next() {
      return null;
    }
  } 
  

Let us understand these methods first!

When we use the enhanced for loop, we are using syntactic sugar:

Iterator<MyType> it = myCollection.iterator();
while (it.hasNext()) {
  MyType element = it.next();
  // do something with element
}

// the loop above is the same as the one below
for(MyType element : myCollection) {
  // do something with element
}

From the while loop, it is clear the next method returns the next element in the iteration. And, hasNext returns true if the iteration has more elements.