Java LinkedList addFirst() Method

Description

The Java LinkedList addFirst(E e) method inserts the specified element E at the front of the linkedList. This method helps in setting the the first element in the list during the course of various add operations.

Declaration

Following is the declaration for java.util.LinkedList.addFirst() method −

public void addFirst(E e)

Parameters

e − The element to be added in the linkedList.

Return Value

This method does not return any value.

Exception

NullPointerException − if the specified element is null.

Adding an Element to the Start of the LinkedList of Integers Example

The following example shows the usage of Java LinkedList addFirst(E) method. In this example, we're using integers. As first, we'll add some items to the linkedList using add() method and then using addFirst() method, we'll add elements to the front of the linkedList. Then we're adding more elements using add() method again and the print the arraydeque to check if insertions in the linkedList are in the order we desired.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {
      
      // create an empty linkedList
      LinkedList<Integer> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add(4);
      linkedList.add(5);
      linkedList.add(6);

      // use addFirst() method to add element at the front of the linkedList
      linkedList.addFirst(3);
      linkedList.addFirst(2);
      linkedList.addFirst(1);//now, element 1 will be at the front

      // these elements will be added in continuation with linkedList.add(6)
      linkedList.add(7);
      linkedList.add(8);

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [1, 2, 3, 4, 5, 6, 7, 8]

Adding an Element to the Start of the LinkedList of Strings Example

The following example shows the usage of Java LinkedList addFirst(E) method. In this example, we're using strings. As first, we'll add some items to the linkedList using add() method and then using addFirst() method, we'll add elements to the front of the linkedList. Then we're adding more elements using add() method again and the print the arraydeque to check if insertions in the linkedList are in the order we desired.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {
      
      // create an empty linkedList
      LinkedList<String> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add("D");
      linkedList.add("E");
      linkedList.add("F");

      // use addFirst() method to add element at the front of the linkedList
      linkedList.addFirst("C");
      linkedList.addFirst("B");
      linkedList.addFirst("A");//now, element A will be at the front

      // these elements will be added in continuation with linkedList.add("F")
      linkedList.add("G");
      linkedList.add("H");

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [A, B, C, D, E, F, G, H]

Adding an Element to the Start of the LinkedList of Objects Example

The following example shows the usage of Java LinkedList addFirst(E) method. In this example, we're using Student objects. As first, we'll add some items to the linkedList using add() method and then using addFirst() method, we'll add elements to the front of the linkedList. Then we're adding more elements using add() method again and the print the arraydeque to check if insertions in the linkedList are in the order we desired.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {

      // create an empty linkedList
      LinkedList<Student> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add(new Student(4, "Julie"));
      linkedList.add(new Student(5, "Robert"));
      linkedList.add(new Student(6, "Adam"));

      // use addFirst() method to add element at the front of the linkedList
      linkedList.addFirst(new Student(3, "Rohan"));
      linkedList.addFirst(new Student(2, "Sohan"));
      linkedList.addFirst(new Student(1, "Mohan"));//now, Student 1 will be at the front

      // these elements will be added in continuation with linkedList.add(new Student(6, "Adam"))
      linkedList.add(new Student(7, "Ali"));
      linkedList.add(new Student(8, "Ahmad"));

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);      
   }
}

class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [[ 1, Mohan ], [ 2, Sohan ], [ 3, Rohan ], [ 4, Julie ], [ 5, Robert ], [ 6, Adam ], [ 7, Ali ], [ 8, Ahmad ]]
java_util_linkedlist.htm
Advertisements