Java ListIterator Interface

The ListIterator interface of the Java collections framework provides the functionality to access elements of a list.

It is bidirectional. This means it allows us to iterate elements of a list in both the direction.

It extends the Iterator interface.

The List interface provides a listIterator() method that returns an instance of the ListIterator interface.

Methods of ListIterator

The ListIterator interface provides methods that can be used to perform various operations on the elements of a list.

• hasNext() - returns true if there exists an element in the list
• next() - returns the next element of the list
• nextIndex() returns the index of the element that the next() method will return
• previous() - returns the previous element of the list
• previousIndex() - returns the index of the element that the previous() method will return
• remove() - removes the element returned by either next() or previous()
• set() - replaces the element returned by either next() or previous() with the specified element

Example 1: Implementation of ListIterator

In the example below, we have implemented the next(), nextIndex() and hasNext() methods of the ListIterator interface in an array list.

 import java.util.ArrayList; import java.util.ListIterator; class Main { public static void main(String[] args) { // Creating an ArrayList ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(1); numbers.add(3); numbers.add(2); System.out.println("ArrayList: " + numbers); // Creating an instance of ListIterator ListIterator<Integer> iterate = numbers.listIterator(); // Using the next() method int number1 = iterate.next(); System.out.println("Next Element: " + number1); // Using the nextIndex() int index1 = iterate.nextIndex(); System.out.println("Position of Next Element: " + index1); // Using the hasNext() method System.out.println("Is there any next element? " + iterate.hasNext()); } } 

Output

 ArrayList: [1, 3, 2] Next Element: 1 Position of Next Element: 1 Is there any next element? true 

Example 2: Implementation of ListIterator

In the example below, we have implemented the previous() and previousIndex() methods of the ListIterator interface in an array list.

 import java.util.ArrayList; import java.util.ListIterator; class Main { public static void main(String[] args) { // Creating an ArrayList ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(1); numbers.add(3); numbers.add(2); System.out.println("ArrayList: " + numbers); // Creating an instance of ListIterator ListIterator<Integer> iterate = numbers.listIterator(); iterate.next(); iterate.next(); // Using the previous() method int number1 = iterate.previous(); System.out.println("Previous Element: " + number1); // Using the previousIndex() int index1 = iterate.previousIndex(); System.out.println("Position of the Previous element: " + index1); } } 

Output

 ArrayList: [1, 3, 2] Previous Element: 3 Position of the Previous Element: 0 

In the above example, initially, the instance of the Iterator was before 1. Since there was no element before 1 so calling the previous() method will throw an exception.

We then used the next() methods 2 times. Now the Iterator instance will be between 3 and 2.

Hence, the previous() method returns 3.