Adding an Element to the Front of LinkedList in Java - GeeksforGeeks

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
// 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();    }}
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.
Java
// 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);    }}
[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:
Java
// 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);    }}
[YOU, ARE, HOW, HI]
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