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Showing content from https://www.tutorialspoint.com/java/util/linkedlist_peek.htm below:

Java LinkedList peek() Method

The Java LinkedList peek() method retrieves the head of the list(but does not remove) represented by this linkedList.Returns null if this linkedList is empty. This method is similar to getFirst() method.

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

public E peek()

NA

This method returns the head of the list represented by this linkedList, or null if this linkedList is empty.

NA

The following example shows the usage of Java LinkedList peek() method with Integers. We're creating an LinkedList of Integers, adding some elements, print it and then use peek() method to get the first element. LinkedList remains untouched.

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(25);
      linkedList.add(30);
      linkedList.add(20);
      linkedList.add(18);        

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

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + linkedList.peek());
	  
      // let us print all the elements available in linkedList again
      System.out.println("LinkedList = " + linkedList);
   }
}

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

LinkedList = [25, 30, 20, 18]
Retrieved Element is = 25
LinkedList = [25, 30, 20, 18]

The following example shows the usage of Java LinkedList peek() method with Strings. We're creating an LinkedList of Strings, adding some elements, print it and then use peek() method to get the first element. LinkedList remains untouched.

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("A");
      linkedList.add("B");
      linkedList.add("C");
      linkedList.add("D");        

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

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + linkedList.peek());
	  
      // let us print all the elements available in linkedList again
      System.out.println("LinkedList = " + linkedList);
   }
}

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

LinkedList = [A, B, C, D]
Retrieved Element is = A
LinkedList = [A, B, C, D]

The following example shows the usage of Java LinkedList peek() method with Student objects. We're creating an LinkedList of Student objects, adding some students, print it and then use peek() method to get the first student. LinkedList remains untouched.

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(1, "Julie"));
      linkedList.add(new Student(2, "Robert"));
      linkedList.add(new Student(3, "Adam"));       

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

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + linkedList.peek());
	  
      // let us print all the elements available in linkedList again
      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 + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

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

LinkedList = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Retrieved Element is = [ 1, Julie ]
LinkedList = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]

java_util_linkedlist.htm

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