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 collection. And, hasNext returns true if there is an element we have not iterated over.