LinkedList in Java

LinkedList is a part of the Java Collection Framework and is present in the java.util package. It implements a doubly-linked list data structure where elements are not stored in contiguous memory. Each node contains two parts: data and references to the next and previous nodes.

• Dynamic Size: LinkedList grows or shrinks dynamically at runtime.
• Maintains Insertion Order: Elements are stored in the order they are added.
• Allows Duplicates: Duplicate elements are allowed.
• Not Synchronized: By default, LinkedList is not thread-safe.
• Efficient Insertion/Deletion: Adding or removing elements at the beginning or middle is faster compared to ArrayList.

import java.util.LinkedList;

public class Geeks {

    public static void main(String[] args){
        
        // Creating a LinkedList
        LinkedList<String> l = new LinkedList<String>();

        // Adding elements to the LinkedList using add() method
        l.add("One");
        l.add("Two");
        l.add("Three");
        l.add("Four");
        l.add("Five");

        System.out.println(l);
    }
}

[One, Two, Three, Four, Five]

Explanation:

• Creates an empty LinkedList of Strings.
• Adds elements "One" to "Five" using the add() method.
• Prints the LinkedList showing elements in insertion order: [One, Two, Three, Four, Five].

Note: LinkedList nodes cannot be accessed directly by index; elements must be accessed by traversing from the head.

Hierarchy of LinkedList

It implements the List and Deque interfaces, both of which are sub-interfaces of the Collection Interface.

Constructors of LinkedList

In order to create a LinkedList, we need to create an object of the LinkedList class. The LinkedList class consists of various constructors that allow the possible creation of the list. The following are the constructors available in this class:

1. LinkedList()

This constructor is used to create an empty linked list. If we wish to create an empty LinkedList with the name list, then it can be created as: 

LinkedList list = new LinkedList();  

2. LinkedList(Collection C)

This constructor is used to create an ordered list that contains all the elements of a specified collection, as returned by the collection's iterator. If we wish to create a LinkedList with the name list, then, it can be created as: 

LinkedList list = new LinkedList(C);

Performing Different Operations on LinkedList

1. Adding Elements

With the help of the add() method, we can add elements to a LinkedList This method can perform multiple operations based on different parameters. They are:  

• add(Object): This method is used to add an element at the end of the LinkedList.
• add(int index, Object): This method is used to add an element at a specific index in the LinkedList.

import java.util.*;

public class Geeks {

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

        ll.add("Geeks");
        ll.add("Geeks");
        ll.add(1, "For");

        System.out.println(ll);
    }
}

[Geeks, For, Geeks]

2. Update Elements

With the help of the set() method, we can update an element in a LinkedList. This method takes an index and the updated element which needs to be inserted at that index.

import java.util.*;

public class Geeks {

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

        ll.add("Geeks");
        ll.add("Geeks");
        ll.add(1, "Geeks");

        System.out.println("Initial LinkedList " + ll);

        ll.set(1, "For");

        System.out.println("Updated LinkedList " + ll);
    }
}

Initial LinkedList [Geeks, Geeks, Geeks]
Updated LinkedList [Geeks, For, Geeks]

3. Removing Elements

Removes the first occurrence of the specified element from the list, if it exists. They are: 

• remove(Object): Removes the first occurrence of the specified object from the LinkedList.
• remove(int index): Removes the element at the given index and shifts subsequent elements.

import java.util.*;

public class Geeks {

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

        ll.add("Geeks");
        ll.add("Geeks");
        ll.add(1, "For");

        System.out.println("Initial LinkedList " + ll);

          // Function call
        ll.remove(1);

        System.out.println("After the Index Removal " + ll);

        ll.remove("Geeks");

        System.out.println("After the Object Removal "
                           + ll);
    }
}

Initial LinkedList [Geeks, For, Geeks]
After the Index Removal [Geeks, Geeks]
After the Object Removal [Geeks]

4. Iterating a LinkedList

There are multiple ways to iterate through LinkedList. The most famous ways are by using the basic for loop in combination with a get() method to get the element at a specific index and the advanced for-loop.

import java.util.*; 
  
public class Geeks { 
  
    public static void main(String args[]) 
    { 
        LinkedList<String> ll 
            = new LinkedList<>(); 
  
        ll.add("Geeks"); 
        ll.add("Geeks"); 
        ll.add(1, "For"); 
  
        // Using the Get method and the for loop 
        for (int i = 0; i < ll.size(); i++) { 
  
            System.out.print(ll.get(i) + " "); 
        } 
  
        System.out.println(); 
  
        // Using the for each loop 
        for (String str : ll) 
            System.out.print(str + " "); 
    } 
} 

Geeks For Geeks 
Geeks For Geeks 

Methods for Java LinkedList

ArrayList vs LinkedList

LinkedList in Java

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