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Adding an Element to the Front of LinkedList in Java
  • Last Updated : 22 Dec, 2020

A Linked  List is a linear data structure, in which the elements are not stored at contiguous memory locations. The elements are linked using pointers and addresses. Each element is known as a node. This article shows how to add an element to the front of LinkedList in Java. 

Method 1: (Using user-defined method)

  • Allocate the memory to a new node.
  • Put in the element to be inserted in the allocated node.
  • Make the next of the new node as the head.
  • Move the head to point to the new node.

Example:

Java

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// Java program to Add an Element
// to the Front of LinkedList
  
import java.io.*;
  
class LinkedList {
    
      // head reference
    Node head;
    
      // Node class
    class Node {
        int data;
        Node next;
  
        Node(int d)
        {
            data = d;
            next = null;
        }
    }
    
    // Inserting node at the front
    public void insertfront(int data)
    {
        // Allocating and inserting the data in that node
        Node new_node = new Node(data);
        
        // Make the next of the newly allocated node to be
        // the head
        new_node.next = head;
        
        // Now make the head to be the newly allocated node
        head = new_node;
    }
    
    // Printing the List
    public void print()
    {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
    }
  
    public static void main(String args[])
    {
          // create a linkedlist
        LinkedList l = new LinkedList();
        
          // insert elements at the front
        l.insertfront(6);
        l.insertfront(5);
        l.insertfront(8);
        l.insertfront(9);
        
          // print the linkedlist
        l.print();
    }
}

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Output

9 8 5 6

Method 2: (Using addFirst(E e) method of LinkedList) 



Declaration:

void addFirst(Object element)

Syntax:

LinkedList.addFirst(e)

Parameters: This function accepts a single parameter element as shown in the above syntax. The element specified by this parameter is appended at beginning of the list.

Return Value: This method does not return any value.

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// Java program to Add an Element
// to the Front of LinkedList
  
import java.util.LinkedList;
  
class AddElementsAtTheFront {
    public static void main(String args[])
    {
          // create a LinkedList
        LinkedList<String> list = new LinkedList<String>();
        
          // add elements at the front
        list.addFirst("HI");
        list.addFirst("HOW");
        list.addFirst("ARE");
        list.addFirst("YOU");
        
          // print LinkedList
        System.out.print(list);
    }
}

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Output

[YOU, ARE, HOW, HI]

Method 3: (Using offerFirst(E e))

This method also inserts the specified element at the front of the list. 

Declaration:

public boolean offerFirst(E e)

Syntax:

LinkedList.offerFirst(e)

Parameters: Here, e is the element to add

Return Value: This method returns true

Example:

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// Java program to Add an Element 
// to the Front of LinkedList
  
import java.util.LinkedList;
  
class AddingElementsAtTheFront {
    
    public static void main(String args[])
    {
          // create a LinkedList
        LinkedList<String> list = new LinkedList<String>();
        
          // add elements at the front
        list.offerFirst("HI");
        list.offerFirst("HOW");
        list.offerFirst("ARE");
        list.offerFirst("YOU");
        
          // print the LinkedList
        System.out.print(list);
    }
}

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Output

[YOU, ARE, HOW, HI]

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