Java LinkedList

In Java, a LinkedList is a doubly linked list implementation in java.util that implements List<E>, Deque<E>, Cloneable, and Serializable. Elements are stored in nodes linked to previous and next nodes. It allows null elements, provides efficient insertions and removals at the list ends and implements standard deque/queue operations (push/pop, offer/poll, addFirst()/addLast()).

Syntax

LinkedList<Type> list = new LinkedList<>();

Parameters:

• Type: The data type of elements stored in the list (eg., String, Integer).

Return value:

• A new empty LinkedList instance of the specified type.

Common Methods in a Linked List

Common methods of LinkedList (inherited from List/Deque or defined in the class) include those for adding, removing, and accessing elements. Here are some of the most frequently used methods with their signatures and brief descriptions:

Example

This example creates a LinkedList of strings and performs various operations on it:

import java.util.LinkedList;

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

    // Adding elements to the LinkedList
    list.add("Alice");      // Append "Alice" to the end
    list.add("Bob");        // Append "Bob" to the end
    list.addFirst("Zara");  // Insert "Zara" at the beginning
    list.addLast("Charlie");// Insert "Charlie" at the end (same as add)

    System.out.println("List after additions: " + list);

    // Accessing elements
    String firstElement = list.getFirst(); // Retrieve first element ("Zara")
    String thirdElement = list.get(2);     // Retrieve element at index 2 ("Bob")
    System.out.println("First element: " + firstElement);
    System.out.println("Element at index 2: " + thirdElement);

    // Removing elements
    list.removeFirst();    // Removes "Zara" (first element)
    list.removeLast();     // Removes "Charlie" (last element)
    list.remove("Alice");  // Removes the first occurrence of "Alice"

    System.out.println("List after removals: " + list);
  }
}

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The output of this code is:

List after additions: [Zara, Alice, Bob, Charlie]
First element: Zara
Element at index 2: Bob
List after removals: [Bob]

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LinkedList vs ArrayList

Rule of thumb:

• Use ArrayList for most cases (better performance & memory).
• Use LinkedList when you need frequent insertions/removals at the beginning or end.