ArrayList listIterator() method example

ArrayList listIterator() returns a list iterator over the elements in this list. It is a bi-directional iterator which is fail-fast in nature.

By default, elements returned by the list iterator are in proper sequence.

1. ArrayList listIterator() method

The listIterator() method is overloaded and comes in two variants:

• ListIterator listIterator() – Returns a list iterator over the elements in this list.
• ListIterator listIterator(int index) – Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list. The specified index indicates the first element that would be returned by an initial call to next. An initial call to previous would return the element with the specified index minus one.

Method parameter – index of the first element to be returned from the list iterator.
Method returns – a list iterator over the elements.
Method throws – IndexOutOfBoundsException – if the index is out of range (less than 0 or greater than list size).

2. ArrayList listIterator() – Iteration

Java program to iterate an arraylist using list iterator obtained through listIterator() method. We will learn to iterate the list in forward and backward direction.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.ListIterator;

public class ArrayListExample 
{
    public static void main(String[] args) throws CloneNotSupportedException 
    {
        ArrayList<String> alphabets = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));
        
        ListIterator<String> listItr = alphabets.listIterator();
        
        System.out.println("===========Forward=========");
        
        while(listItr.hasNext()) {
            System.out.println(listItr.next());
        }
        
        System.out.println("===========Backward=========");
        
        while(listItr.hasPrevious()) {
            System.out.println(listItr.previous());
        }
    }
}

Program output.

===========Forward=========
A
B
C
D
===========Backward=========
D
C
B
A

3. ArrayList listIterator() – Add/Remove

ListIterator supports to add and remove elements in the list while we are iterating over it.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.ListIterator;

public class ArrayListExample 
{
    public static void main(String[] args) throws CloneNotSupportedException 
    {
        ArrayList<String> alphabets = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));
        
        ListIterator<String> listItr = alphabets.listIterator();
        
        System.out.println(listItr.next());		//A
        System.out.println(listItr.next());		//B
        
        listItr.add("E");       
        
        System.out.println(alphabets); //["A", "B", "E", "C", "D"]
        
        System.out.println(listItr.previous());	//E
        System.out.println(listItr.next());		//E
        
        System.out.println(listItr.next());		//C
        
        listItr.remove();       
        
        System.out.println(alphabets); //["A", "B", "E", "D"]
        
        System.out.println(listItr.next());		//D
    }
}

Program output.

A
B
[A, B, E, C, D]
E
E
C
D
[A, B, E, D]

4. ArrayList listIterator() – Fail fast

ListIterator is fail fast. It means if we modibt the arraylist after list iterator is created, then it will throw ConcurrentModificationException on next() or previous() method call.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.ListIterator;

public class ArrayListExample 
{
    public static void main(String[] args) throws CloneNotSupportedException 
    {
        ArrayList<String> alphabets = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));
        
        ListIterator<String> listItr = alphabets.listIterator();
        
        System.out.println(listItr.next());     //A
        System.out.println(listItr.next());     //B
            
        alphabets.add("E");       
        
        System.out.println(alphabets);          //["A", "B", "C", "D", "E"]
        
        System.out.println(listItr.next());     //Error
    }
}

Program output.

A
B
[A, B, C, D, E]
Exception in thread "main" java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
	at java.util.ArrayList$Itr.next(ArrayList.java:851)
	at com.howtodoinjava.example.ArrayListExample.main(ArrayListExample.java:22)

5. Differences between Iterator and ListIterator

That’s all for the ArrayList listIterator() method in Java.

Happy Learning !!

Read More:

A Guide to Java ArrayList
ArrayList Java Docs
ListIterator Java Docs