- Java.util Package Classes
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- Java.util - Hashtable
- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
- Java.util - LinkedList
- Java.util - ListResourceBundle
- Java.util - Locale
- Java.util - Observable
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- Java.util - Properties
- Java.util - PropertyPermission
- Java.util - PropertyResourceBundle
- Java.util - Random
- Java.util - ResourceBundle
- Java.util - ResourceBundle.Control
- Java.util - Scanner
- Java.util - ServiceLoader
- Java.util - SimpleTimeZone
- Java.util - Stack
- Java.util - StringTokenizer
- Java.util - Timer
- Java.util - TimerTask
- Java.util - TimeZone
- Java.util - TreeMap
- Java.util - TreeSet
- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util Package Extras
- Java.util - Interfaces
- Java.util - Exceptions
- Java.util - Enumerations
- Java.util Useful Resources
- Java.util - Useful Resources
- Java.util - Discussion
Java LinkedList peekFirst() Method
Description
The Java LinkedList peekFirst() method retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
Declaration
Following is the declaration for java.util.LinkedList.peekFirst() method
public E peekFirst()
Parameters
NA
Return Value
This method returns the first element of this list, or null if this list is empty.
Exception
NA
Getting the First Element of the LinkedList of Integers Example
The following example shows the usage of Java LinkedList peekFirst() method with Integers. We're creating an LinkedList of Integers, adding some elements, print it and then use peekFirst() 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.peekFirst()); // let us print all the elements available in linkedList again System.out.println("LinkedList = " + linkedList); } }
Output
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]
Getting the First Element of the LinkedList of Strings Example
The following example shows the usage of Java LinkedList peekFirst() method with Strings. We're creating an LinkedList of Strings, adding some elements, print it and then use peekFirst() 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.peekFirst()); // let us print all the elements available in linkedList again 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] Retrieved Element is = A LinkedList = [A, B, C, D]
Getting the First Element of the LinkedList of Objects Example
The following example shows the usage of Java LinkedList peekFirst() method with Student objects. We're creating an LinkedList of Student objects, adding some students, print it and then use peekFirst() 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.peekFirst()); // 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); } }
Output
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 ]]
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