Iterate over LinkedList using an Iterator in Java

In this article, we will discuss how to iterate over a LinkedList using an Iterator in Java. We will cover the basics of using an Iterator, providing examples to demonstrate its usage.

Table of Contents

1. Introduction
2. Using an Iterator to Iterate Over a LinkedList
3. Removing Elements During Iteration
4. Complete Example
5. Conclusion

Introduction

A LinkedList in Java is a part of the Java Collections Framework and implements the List and Deque interfaces. It allows for efficient insertion and removal of elements. Using an Iterator to traverse a LinkedList provides a flexible way to access each element and optionally remove elements during iteration.

Using an Iterator to Iterate Over a LinkedList

The Iterator interface provides methods to iterate over a collection. The hasNext() method checks if there are more elements to iterate, and the next() method returns the next element in the iteration.

Example

import java.util.Iterator;
import java.util.LinkedList;

public class IterateUsingIterator {
    public static void main(String[] args) {
        LinkedList<String> fruits = new LinkedList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");

        // Creating an iterator
        Iterator<String> iterator = fruits.iterator();

        // Iterating over the LinkedList
        while (iterator.hasNext()) {
            String fruit = iterator.next();
            System.out.println("Fruit: " + fruit);
        }
    }
}

Output:

Fruit: Apple
Fruit: Banana
Fruit: Orange

Removing Elements During Iteration

The Iterator interface also provides a remove() method, which can be used to remove elements from the collection during iteration. This is particularly useful when you need to filter elements based on certain criteria.

Example

import java.util.Iterator;
import java.util.LinkedList;

public class RemoveDuringIteration {
    public static void main(String[] args) {
        LinkedList<String> fruits = new LinkedList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Banana");

        // Creating an iterator
        Iterator<String> iterator = fruits.iterator();

        // Iterating and removing "Banana" from the LinkedList
        while (iterator.hasNext()) {
            String fruit = iterator.next();
            if ("Banana".equals(fruit)) {
                iterator.remove();
            }
        }

        // Printing the LinkedList after removal
        System.out.println("LinkedList after removal: " + fruits);
    }
}

Output:

LinkedList after removal: [Apple, Orange]

Complete Example

Here is a complete example that demonstrates both iterating over a LinkedList and removing elements during iteration.

import java.util.Iterator;
import java.util.LinkedList;

public class LinkedListIteratorExample {
    public static void main(String[] args) {
        LinkedList<String> fruits = new LinkedList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Banana");

        // Creating an iterator
        Iterator<String> iterator = fruits.iterator();

        // Iterating over the LinkedList
        System.out.println("Iterating over the LinkedList:");
        while (iterator.hasNext()) {
            String fruit = iterator.next();
            System.out.println("Fruit: " + fruit);
        }

        // Re-create iterator for removal example
        iterator = fruits.iterator();

        // Iterating and removing "Banana" from the LinkedList
        while (iterator.hasNext()) {
            String fruit = iterator.next();
            if ("Banana".equals(fruit)) {
                iterator.remove();
            }
        }

        // Printing the LinkedList after removal
        System.out.println("LinkedList after removal: " + fruits);
    }
}

Output:

Iterating over the LinkedList:
Fruit: Apple
Fruit: Banana
Fruit: Orange
Fruit: Banana
LinkedList after removal: [Apple, Orange]

Conclusion

Using an Iterator to traverse a LinkedList in Java provides a flexible way to access and manipulate elements. This guide provided examples to demonstrate how to use an Iterator to iterate over a LinkedList and remove elements during iteration. By understanding these concepts, you can efficiently manage elements in your LinkedList.