Introduction

• LinkedList is an implemented class of the List and Deque interfaces.
• It is present in the java.util package.
• It was introduced in JDK 1.2 version.

• Hierarchy:
  • 

• Syntax :-

  package java.util;
  
  public class LinkedList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable
  {    
      // Constructors
      
      // Methods
      
      // Fields
  }

  • LinkedList implements both List and Deque interfaces, so it can be used as a list, queue, or stack.
  • It does not implement RandomAccess, so accessing elements by index is slower compared to ArrayList.

• LinkedList is a doubly-linked list data structure that allows efficient insertion and deletion of elements.
  
  

Constructors of LinkedList Class

• Below are the constructors defined in the LinkedList class:

Methods of LinkedList Class

• Below are some methods defined specifically in the LinkedList class:

Program :

• In below program, we are directly using LinkedList class.

• import java.util.LinkedList;
  
  public class LinkedListDemo
  {
      public static void main(String[] args)
      {
          LinkedList<String> list = new LinkedList<>();
  
          // Adding elements
          list.add("Apple");
          list.add("Banana");
          list.add("Mango");
          list.add("Banana"); // duplicate allowed
  
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Accessing first and last elements
          System.out.println("First Element: " + list.getFirst());
          System.out.println("Last Element: " + list.getLast());
  
          System.out.println("-------------------------");
  
          // Updating element
          list.set(1, "Orange");
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Removing element
          list.remove("Apple");
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Using LinkedList as a Queue
          list.addFirst("Grapes");
          list.addLast("Pineapple");
          System.out.println(list);
  
          System.out.println("-------------------------");
  
          // Iterating LinkedList
          for(String fruit : list)
          {
              System.out.println(fruit);
          }
      }
  }

  Output:

  [Apple, Banana, Mango, Banana]
  -------------------------
  First Element: Apple
  Last Element: Banana
  -------------------------
  [Apple, Orange, Mango, Banana]
  -------------------------
  [Orange, Mango, Banana]
  -------------------------
  [Grapes, Orange, Mango, Banana, Pineapple]
  -------------------------
  Grapes
  Orange
  Mango
  Banana
  Pineapple

Properties of LinkedList Class:

1. LinkedList is a linear data structure that stores elements in nodes, where each node contains data and references (links) to the next and previous node.
2. LinkedList implements both the List and Deque interfaces, so it can be used as a list, queue, or stack.
3. LinkedList can store heterogeneous elements if generics are not used.
4. It allows storing of duplicate elements.
5. It allows storing of null values.
6. Insertion order is preserved, meaning elements are retrieved in the same sequence they were added.
7. Sorting order is not maintained; explicit sorting is required using Collections.sort() or list.sort().
8. LinkedList is non-synchronized and not thread-safe.
9. Like ArrayList, it does not guarantee data consistency in multi-threaded environments.