Java.util.LinkedList.peek() , peekfirst(), peeklast() in Java

10 Dec, 2018
Linked list class offers the functionality to “look into” the first and last elements of the list and hence can be useful in cases where only the retrieval is required and not necessarily the deletion is required. Three functionalities are present and all are discussed in this article. 1. peek() : This method retrieves, but does not remove, the head (first element) of this list.
Declaration : 
   public E peek()
Return Value : 
  This method returns the head of this list, or null if this list is empty.

// Java code to demonstrate the working// of peek() in LinkedListimport java.util.*;public class LinkedPeek1 {  public static void main(String[] args)    {        // declaring a LinkedList        LinkedList list = new LinkedList();          // adding  elements        list.add("Geeks");        list.add(4);        list.add("Geeks");        list.add("8");          // printing the list        System.out.println("The initial list is :" + list);          // peek at the head of the list        // Prints 1st element, "Geeks"        System.out.println("Head of the list : " + list.peek());    }}
Output:
The initial list is :[Geeks, 4, Geeks, 8]
Head of the list : Geeks

2. peekFirst() : This method retrieves, but does not remove, the first element of this list, or returns null if this list is empty. This works similar to peek().
Declaration : 
   public E peekFirst()
Return Value : 
    This method returns the first element of this list, or null if this list is empty

// Java code to demonstrate the working// of peekFirst() in LinkedListimport java.util.*;public class LinkedPeek2 {  public static void main(String[] args)    {        // declaring a LinkedList        LinkedList list = new LinkedList();          // adding  elements        list.add("Geeks");        list.add(4);        list.add("Geeks");        list.add("8");          // printing the list        System.out.println("The initial list is :" + list);          // peek at the first element of the list        // Prints 1st element, "Geeks"        System.out.println("First element of the list is : " + list.peekFirst());    }}
Output:
The initial list is :[Geeks, 4, Geeks, 8]
First element of the list is : Geeks

3. peekLast() : This method retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
Declaration
  public E peekLast()
Return Value
   This method returns the last element of this list, or null if this list is empty

// Java code to demonstrate the working// of peekLast() in LinkedListimport java.util.*;public class LinkedPeek3 {  public static void main(String[] args)    {        // declaring a LinkedList        LinkedList list = new LinkedList();          // adding  elements        list.add("Geeks");        list.add(4);        list.add("Geeks");        list.add(8);          // printing the list        System.out.println("The initial list is :" + list);          // peek at the last element of the list        // Prints last element, 8        System.out.println("Last element of the list is : " + list.peekLast());    }}
Output:
The initial list is :[Geeks, 4, Geeks, 8]
Last element of the list is : 8

Practical Application : The practical application that can be thought of is that this can be used in potentially the game of cards where the individuals can peek the first or last element of the deck on asking which element they want to see. Code below explains the working.
// Java code to demonstrate the application// of peek()import java.util.*;public class LinkedPeekApp {  public static void main(String[] args)    {          // declaring a LinkedList        LinkedList list = new LinkedList();          // adding  elements in deck        list.add(5);        list.add(4);        list.add("Jack");        list.add(8);        list.add("King");          // printing the list        System.out.println("The initial deck is :" + list);          String d = "upper";          System.out.println("The element chosen to peek is : " + d);          if (d == "upper")            System.out.println("The Upper element is : " + list.peekFirst());        else            System.out.println("The Lower element is : " + list.peekLast());    }}
Output :
The initial deck is :[5, 4, Jack, 8, King]
The element chosen to peek is : upper
The Upper element is : 5

This article is contributed by Astha Tyagi. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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