Java LinkedList is an implementation class of List interface in Collection Framework. It implements a doubly-linked(data structure) list internally to store data. It allows to perform all list operations and permits all elements including null value.
It was added in the Java 1.2 version and is located in java.util package of java.base module. In this article, we will see some example to understand the working of LinkedList. The syntax of the class is like:
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, SerializableLet's start with creating a LinkedList and add elements to it by using the add() method. Here, we are creating a collection of student data and storing it into a LinkedList.
import java.util.LinkedList;
/*
* Code example to create LinkedList in Java
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
System.out.println(students);
}
}Output:
[Kunal, Rohan, David]
To create a LinkedList, the LinkedList class provides two constructors. one is used to create an empty list while the other is used to create LinkedList with elements of a collection such as ArrayList. Let's see the table below.
| Constructor | Description |
|---|---|
| LinkedList() | It is used to construct an empty list. |
| LinkedList​(Collection<? extends E> c) | It is used to construct a list containing the elements of the specified collection, in the order, they are returned by the collection's iterator. |
Here, we used the second constructor to create LinkedList from the list elements. It is helpful when we want to create LinkedList from the existing collections such as list, set, etc.
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
/*
* Code example to create LinkedList from other collection(list) in Java
*/
public class JExercise {
public static void main(String[] args) {
List<String> list = Arrays.asList("Kunal","Rohan","David");
// Get LinkedList from a List
LinkedList<String> students = new LinkedList<String>(list);
System.out.println(students);
}
}Output:
[Kunal, Rohan, David]
LinkedList allows all the common operations such as adding, removing and accessing elements. Here, we will see some examples to work with LinkedList.
LinkedList class provides several methods to add elements such as add() method add the elements in a sequence while the addFirst() method adds the elements at the starting of LInkedLIst and addLast() method adds the elements at the end of LInkedList. We can use these methods according to the need. See the example where we used all these methods.
import java.util.LinkedList;
/*
* Code example to create LinkedList and elements in Java
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
System.out.println(students);
// Adding element at starting of list
students.addFirst("Mohan");
System.out.println(students);
// Adding element at specified index
students.add(2,"John");
System.out.println(students);
// Adding element at end of the list
students.addLast("Hemant");
System.out.println(students);
}
}Output:
[Kunal, Rohan, David]
[Mohan, Kunal, Rohan, David]
[Mohan, Kunal, John, Rohan, David]
[Mohan, Kunal, John, Rohan, David, Hemant]
LinkedList class provides several methods to remove elements such as remove() method remove the elements in a sequence while the removeFirst() method removes the elements from the starting of LInkedLIst and removeLast() method removes the elements from the end of LInkedList. We can use these methods according to the need. See the example where we used all these methods.
import java.util.LinkedList;
/*
* Code example to create LinkedList and elements in Java
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
System.out.println(students);
// Remove first element
students.removeFirst();
System.out.println(students);
// Remove from specified index
students.remove(1);
System.out.println(students);
// Remove last element
students.removeLast();
System.out.println(students);
}
}Output:
[Kunal, Rohan, David]
[Rohan, David]
[Rohan]
[]
Like adding and removing methods, LinkedList class provides several accessibility methods as well such as get() method gets the elements in a sequence while the getFirst() method returns the elements of the starting of LInkedLIst and getLast() method returns the elements from the end of LInkedList. We can use these methods according to the need. See the example where we used all these methods.
import java.util.LinkedList;
/*
* Code example to create LinkedList and Access elements
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String>students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
System.out.println(students);
System.out.println(students.size());
// Get first element
String fName = students.getFirst();
System.out.println(fName);
// Get last element
String lName = students.getLast();
System.out.println(lName);
// Get element of specified index
System.out.println(students.get(1));
}
}Output:
[Kunal, Rohan, David]
3
Kunal
David
Rohan
To traverse all the elements of the LinkedList, we can use any loop such as for loop, for-each loop, etc. See, in the below example, we used both to traverse LinkedList.
import java.util.LinkedList;
/*
* Code example to create LinkedList and Traverse it
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
// Traversing using for loop
System.out.println("Traversing using for loop");
for (int i = 0; i < students.size(); i++) {
System.out.println(students.get(i));
}
// Traversing using for-each loop
System.out.println("\nTraversing using for-each loop");
for(String name: students) {
System.out.println(name);
}
}
}Output:
Traversing using for loop
Kunal
Rohan
David
Traversing using for-each loop
Kunal
Rohan
David
Iterator is an interface in Collection framework which gives iteration feature to all the collection implementation classes such as ArrayList, LInkedList, etc.
import java.util.Iterator;
import java.util.LinkedList;
/*
* Code example to create LinkedList
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> students = new LinkedList<String>();
students.add("Kunal");
students.add("Rohan");
students.add("David");
// Traversing using iterator
System.out.println("Traversing using Iterator");
Iterator<String> itr = students.iterator();
while(itr.hasNext()) {
System.out.println(itr.next());
}
}
}Output:
Traversing using Iterator
Kunal
Rohan
David
The LinkedList class provides one more method set() that is used to modify any element in the LInkedList. This method takes two arguments, one is index and the second is value. So, the value will be replaced at the specified index location. See the example below.
import java.util.LinkedList;
/*
* Code example to create LinkedList
*/
public class JExercise {
public static void main(String[] args) {
LinkedList<String> linkedList = new LinkedList<String>();
linkedList.add("Sohan");
linkedList.add("Mohan");
linkedList.add("Mac");
linkedList.add("David");
System.out.println(linkedList);
// Modify element
linkedList.set(2,"Shubham");
System.out.println(linkedList);
linkedList.set(3, "Jack");
System.out.println(linkedList);
// Get size of linkedlist
int size = linkedList.size();
System.out.println(size);
}
}Output:
[Sohan, Mohan, Mac, David]
[Sohan, Mohan, Shubham, David]
[Sohan, Mohan, Shubham, Jack]
4
