What’s the Difference Between Iterator and ListIterator?

What is Listiterator?

ListIterator is a Collection framework interface that extends the Iterator interface. ListIterator allows you to traverse the Collection's elements in forward and backward ways. Any Collection component can also be added, removed, or modified. In a nutshell, it eliminates the shortcomings of the Iterator.

Listiterator Syntax

import java.util.*;

// Here "y" is any List object.
// "lit" is of type ListIterator interface and refers to "y"
ListIterator lit = y.listIterator();

Differentiation between Iterator and ListIterator

To make it easy for you to understand Iterator vs listIterator,  the difference between them has been represented in tabular form below:

Methods in Iterator vs ListIterator

Methods in Iterator:

• hasNext() - It returns true if the iteration has more elements.
• next() - This method returns the next element in the iteration.
• remove() - This method removes the last element that is returned by the Iterator from the Collection.
   

After Java 17 release, in addition to the above-listed methods, we have four methods in the ListIterator interface that are not found in the Iterator:

• hasPrevious() - It returns the previous object in an ordered list
• nextIndex() - It returns the numeric index of the element that is next in the list
• previousIndex() - It returns the numeric index of the previous element in the ordered list
• add() - It inserts an object into an ordered list at a specific location

Dry Run

Importing java.util package:

Taking user input:

Forward traversal using iterator:

Forward and Backward traversal using Listiterator:

Example for Iterator

The code below explains how to use Iterator with all the important methods available.

Code:

• Java

Java

// Importing the ArrayList class and the Iterator class
import java.util.*;

public class Main {
  public static void main(String[] args) {

    // Making a collection
    ArrayList < String > countries = new ArrayList < String > ();
    Scanner scanner = new Scanner(System.in);
    
    System.out.print("Enter 5 countries :\n");
    for (int i = 0; i < 5; i++) 
    {
      countries.add(scanner.nextLine());
    }
    System.out.println("The countries are:");
    System.out.println(countries);

    // Get the iterator
    Iterator < String > it = countries.iterator();

    // Print the first item using next() method
    System.out.println(it.next());
    System.out.println("Looping through a collection using next() and hasNext() methods");
    
    // Looping through the collection using next() and hasNext() methods
    while (it.hasNext()) {
      System.out.println(it.next());
    }
    
    // Using the remove() method
    it.remove();
    System.out.println("Looping through a collection using next() and hasNext() methods again");
    
    // Looping through the collection after using remove() method
    while (it.hasNext()) {
      System.out.println(it.next());
    }
    System.out.println("-------elements are removed-------");
  }
}

You can also try this code with Online Java Compiler

Run Code

Output:

Practice by yourself on java online compiler.

Example for ListiIterator

The code below explains how to use a listIterator.

Code:

• Java

Java

import java.util.*;

public class Main {
  	public static void main(String args[]) 
  	{
   		// Making a collection
    	ArrayList < String > countries = new ArrayList < String > ();
     	Scanner scanner = new Scanner(System.in); 
     	System.out.print("Enter 5 countries :\n");
        for (int i = 0; i < 5; i++) 
        {      
            countries.add(scanner.nextLine()); 
        } 
        System.out.println("The countries are:");
        System.out.println(countries); 

    	// Getting the ListIterator object.
    	ListIterator listIterator = countries.listIterator();

    	// Print the ArrayList elements in forward direction.
    	System.out.println("ArrayList elements in " + "forward direction:");
    	while (listIterator.hasNext()) {
      		System.out.println(listIterator.next());
    	}

    	// Print the ArrayList elements in backward direction.
    	System.out.println("ArrayList elements in " + "backward direction:");
    	while (listIterator.hasPrevious()) {
      		System.out.println(listIterator.previous());
    	}
  	}
}

You can also try this code with Online Java Compiler

Run Code

Output:

Class Diagram for Iterator vs Listiterator

Which One to Use?

When the underlying Collection class is numerically ordered and at least one of the following three conditions is true, developers should pick the ListIterator over the Iterator:

• A class is needed to be added to a specific location in the ordered Collection.
• Backward navigation through an ordered Collection is required.
• Finding the numerical index of the previous or following element in an ordered Collection is required.

Frequently Asked Questions

What is the connection between the Iterator and ListIterator interfaces?

In Java, an Iterator interface allows us to traverse the elements of a list in the forward direction. In contrast, a ListIterator interface extends the Iterator interface and allows us to traverse the elements in both the forward and backward ways.

Is Iterator a class or an interface?

The Java Iterator is an interface that was introduced in the Java Programming language as part of the Java 1.2 Collection architecture. It is part of Java.util package.

What is the difference between iterator and ListIterator in Python?

The key difference is ListIterator is specific to lists, offering bidirectional traversal and modification, while iterators generally traverse elements one by one in a forward direction from any iterable.

What is the difference between iterator and enumerator?

An iterator is a more general concept for iterating over elements, while an enumerator provides index-value pairs during iteration, common in Python's enumerate() function.

What is the main difference between iterator and iterable?

Iterators are objects that allow iteration over a sequence, while iterables are objects that can be iterated over, such as lists or dictionaries. An iterator is created from an iterable.

Conclusion

In this blog, we have discussed what’s the difference between Iterator and ListIterator. Knowing the difference between Iterator and ListIterator in Java is really important for writing better programs. Iterator is like a general tool for moving through collections, while ListIterator is more specialized for lists and offers extra features. 

To explore more interesting coding-related articles, refer to the following links:

• Java List Iterator
• C++ String concatenation
• Byte array to string
• Enqueue and dequeue in C
• Difference Between Rank and Dense Rank
   

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