Topic 13330 min readStructured Tutorial

Java LinkedList Tutorial

Quick Answer

LinkedList explains in Java, LinkedList is a part of the Java Collections Framework and provides a doubly linked list implementation.

Learning Objectives

Explain the purpose of LinkedList in a practical learning context.
Identify the main ideas, terms, and decisions involved in LinkedList.
Apply LinkedList in a simple real-world scenario or practice task.

Introduction to Java LinkedList

In Java, LinkedList is a part of the Java Collections Framework and provides a doubly linked list implementation.

It allows efficient insertion and removal of elements from any position in the list.

This tutorial will guide you through the basics of LinkedList, its key methods, and practical usage.

LinkedList offers flexibility and performance for dynamic data management.

What is a LinkedList?

A LinkedList is a linear data structure where each element is a separate object called a node.

Each node contains data and references (links) to the next and previous nodes in the sequence.

Unlike arrays, LinkedLists do not store elements in contiguous memory locations.

Doubly linked: nodes link to both next and previous nodes.
Dynamic size: grows and shrinks as needed.
Efficient insertions and deletions at any position.

Java LinkedList Class Overview

Java provides the LinkedList class in the java.util package.

It implements List, Deque, and Queue interfaces, making it versatile for different use cases.

Supports all optional List operations.
Can be used as a list, stack, or queue.
Allows null elements.

Java LinkedList Interfaces
Interface	Purpose
List	Ordered collection with positional access
Deque	Double-ended queue allowing element insertion/removal at both ends
Queue	First-in-first-out data structure

Key Methods of LinkedList

LinkedList provides many useful methods for manipulating elements.

Here are some of the most commonly used ones.

add(E e): Adds element to the end.
addFirst(E e): Inserts element at the beginning.
addLast(E e): Inserts element at the end.
remove(): Removes and returns the first element.
remove(Object o): Removes the first occurrence of the specified element.
get(int index): Returns element at specified position.
getFirst(): Returns the first element.
getLast(): Returns the last element.
size(): Returns the number of elements.

When to Use LinkedList in Java

LinkedList is ideal when your application requires frequent insertions and deletions from the list.

It performs better than ArrayList for add/remove operations at the beginning or middle of the list.

Use LinkedList if you need constant-time insertions/removals at both ends.
Avoid LinkedList if you need fast random access; ArrayList is better for that.
LinkedList uses more memory due to storing node pointers.

Example: Using Java LinkedList

Let's see a simple example demonstrating basic LinkedList operations.

Practical Example

This example creates a LinkedList of strings, adds elements at different positions, accesses first and last elements, removes elements, and iterates through the list.

Examples

Basic LinkedList Operations in Java

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        LinkedList<String> fruits = new LinkedList<>();

        // Adding elements
        fruits.add("Apple");
        fruits.addFirst("Mango");
        fruits.addLast("Banana");

        // Accessing elements
        System.out.println("First fruit: " + fruits.getFirst());
        System.out.println("Last fruit: " + fruits.getLast());

        // Removing elements
        fruits.remove("Mango");
        fruits.removeFirst();

        // Iterating over elements
        for (String fruit : fruits) {
            System.out.println(fruit);
        }
    }
}

This example creates a LinkedList of strings, adds elements at different positions, accesses first and last elements, removes elements, and iterates through the list.

Best Practices

Use LinkedList when you have many insertions and deletions in the middle of the list.
Prefer ArrayList if you need fast random access by index.
Avoid unnecessary conversions between LinkedList and other collections.
Use generics to specify the type of elements stored in the LinkedList.
Always check for null elements if your logic depends on non-null values.

Common Mistakes

Using LinkedList when frequent random access is required, leading to poor performance.
Not handling null elements properly, causing NullPointerExceptions.
Modifying the list while iterating without using an iterator's remove method.
Assuming LinkedList is always faster than ArrayList for all operations.

Hands-on Exercise

Implement a Stack Using LinkedList

Use Java's LinkedList to implement a stack with push, pop, and peek operations.

Expected output: A working stack implementation using LinkedList.

Hint: Use LinkedList's addFirst and removeFirst methods to simulate stack behavior.

Compare Performance of ArrayList and LinkedList

Write a Java program to compare insertion and access times between ArrayList and LinkedList.

Expected output: Performance comparison results printed to console.

Hint: Use System.nanoTime() to measure elapsed time for operations.

Interview Questions

What is the difference between ArrayList and LinkedList in Java?

Interview

ArrayList uses a dynamic array to store elements, providing fast random access but slower insertions and deletions in the middle. LinkedList uses a doubly linked list structure, offering faster insertions and deletions but slower random access.

Can LinkedList contain null elements?

Interview

Yes, Java's LinkedList implementation allows null elements.

Which interfaces does Java's LinkedList implement?

Interview

LinkedList implements List, Deque, and Queue interfaces.