LinkedList In Java | Java Tutorial

ByRajkumar Updated on

Earlier we have seen Arrays and ArrayList. In this post, we will see LinkedList in Java. LinkedList is a class in the Collection Framework. LinkedList class implements List and Deque interfaces. LinkedList class extends AbstractList class. Lets see some key points on LinkedList.

  • LinkedList class can hold duplicate elements in list.
  • LinkedList is used to create an empty linked list.
  • LinkedList class maintains insertion order.
  • LinkedList class is non synchronized.
  • In LinkedList class, manipulation is fast because shifting is not required when new element is inserted or deleted from the list.

Java LinkedList Example:

package samplePackage;

import java.util.LinkedList;

public class LinkedListExample {
	
	public static void main(String args[]) {
	
		//Creating linked list object
		LinkedList<String> lref = new LinkedList<String>();
		// Adding elements using add method
		lref.add("IDE");
		lref.add("RC");
		lref.add("WebDriver");
		lref.add("Grid");
		System.out.println(lref);
		
		// Adding element at first position in list using addFirst
		lref.addFirst("QTP");
		// Adding element at last position in list using addLast
		lref.addLast("Protractor");
		System.out.println(lref);
		
		// Add elements at index 1 in list
		lref.add(0, "Mercury");
		System.out.println(lref);
		
		// Removing first item from list using removeFirst method
		lref.removeFirst();
		// Removing last item from list using removeLast method.
		lref.removeLast();
		System.out.println(lref);
		
		// Removing item from list using value
		lref.remove("Two");
		System.out.println(lref);
		// Removing item from list using index
		lref.remove(3);
		System.out.println(lref);
		// Get item from list using index
		System.out.println(lref.get(0));
		// Set item at given index in list
		lref.set(3, "New Entry");
		System.out.println(lref);
		
		// We have four ways to print all the values of linked list
		
		System.out.println("====== For Loop starts here ======");
		for(int l=0; l<lref.size(); l++) {
			System.out.println(lref.get(l));
		}
		System.out.println("====== For Loop ends here ======");
		
		System.out.println("====== For Each starts here ======");
		for(String str:lref) {
			System.out.println(str);
		}
		System.out.println("====== For Each ends here ======");
		
		System.out.println("====== Iterator starts here ======");
		Iterator <String> it = lref.iterator();
		while(it.hasNext()){
			System.out.println(it.next());
		}		
		System.out.println("====== Iterator ends here ======");
		
		System.out.println("====== While starts here ======");

		int num=0;
		while(lref.size()>num){
			System.out.println(lref.get(num));
			num=num+1;
		}		
		System.out.println("====== While ends here ======");
		
	}
	
}

Output:

[IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid, Protractor]
[Mercury, QTP, IDE, RC, WebDriver, Grid, Protractor]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, Grid]
QTP
[QTP, IDE, RC, New Entry]

LinkedList using For loop:

Output:

[IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid, Protractor]
[Mercury, QTP, IDE, RC, WebDriver, Grid, Protractor]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, Grid]
QTP
[QTP, IDE, RC, New Entry]
====== For Loop starts here ======
QTP
IDE
RC
New Entry
====== For Loop ends here ======

LinkedList with Enhanced For Loop:

package samplePackage;

import java.util.LinkedList;

public class LinkedListExample {
	
	public static void main(String args[]) {
	
		//Creating linked list object
		LinkedList<String> lref = new LinkedList<String>();
		// Adding elements using add method
		lref.add("IDE");
		lref.add("RC");
		lref.add("WebDriver");
		lref.add("Grid");
		System.out.println(lref);
		
		// Adding element at first position in list using addFirst
		lref.addFirst("QTP");
		// Adding element at last position in list using addLast
		lref.addLast("Protractor");
		System.out.println(lref);
		
		// Add elements at index 1 in list
		lref.add(0, "Mercury");
		System.out.println(lref);
		
		// Removing first item from list using removeFirst method
		lref.removeFirst();
		// Removing last item from list using removeLast method.
		lref.removeLast();
		System.out.println(lref);
		
		// Removing item from list using value
		lref.remove("Two");
		System.out.println(lref);
		// Removing item from list using index
		lref.remove(3);
		System.out.println(lref);
		// Get item from list using index
		System.out.println(lref.get(0));
		// Set item at given index in list
		lref.set(3, "New Entry");
		System.out.println(lref);
		System.out.println("====== Enhanced For loop starts here ======");
		for(String str:lref) {
			System.out.println(str);
		}
		System.out.println("====== Enhanced For loop ends here ======");
	}
	
}
Output:
[IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid, Protractor]
[Mercury, QTP, IDE, RC, WebDriver, Grid, Protractor]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, Grid]
QTP
[QTP, IDE, RC, New Entry]
====== Enhanced For loop starts here ======
QTP
IDE
RC
New Entry
====== Enhanced For loop ends here ======

LinkedList using Iterator:

package samplePackage;

import java.util.Iterator;
import java.util.LinkedList;

public class LinkedListExample {
	
	public static void main(String args[]) {
	
		//Creating linked list object
		LinkedList<String> lref = new LinkedList<String>();
		// Adding elements using add method
		lref.add("IDE");
		lref.add("RC");
		lref.add("WebDriver");
		lref.add("Grid");
		System.out.println(lref);
		
		// Adding element at first position in list using addFirst
		lref.addFirst("QTP");
		// Adding element at last position in list using addLast
		lref.addLast("Protractor");
		System.out.println(lref);
		
		// Add elements at index 1 in list
		lref.add(0, "Mercury");
		System.out.println(lref);
		
		// Removing first item from list using removeFirst method
		lref.removeFirst();
		// Removing last item from list using removeLast method.
		lref.removeLast();
		System.out.println(lref);
		
		// Removing item from list using value
		lref.remove("Two");
		System.out.println(lref);
		// Removing item from list using index
		lref.remove(3);
		System.out.println(lref);
		// Get item from list using index
		System.out.println(lref.get(0));
		// Set item at given index in list
		lref.set(3, "New Entry");
		System.out.println(lref);
		
                System.out.println("====== Iterator starts here ======");
		Iterator <String> it = lref.iterator();
		while(it.hasNext()){
			System.out.println(it.next());
		}		
		System.out.println("====== Iterator ends here ======");		
	}
	
}

Output:

[IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid, Protractor]
[Mercury, QTP, IDE, RC, WebDriver, Grid, Protractor]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, WebDriver, Grid]
[QTP, IDE, RC, Grid]
QTP
[QTP, IDE, RC, New Entry]
====== Iterator starts here ======
QTP
IDE
RC
New Entry
====== Iterator ends here ======

Methods for Java LinkedList:

  • int size(): It returns the number of elements in the list.
  • void clear(): It removes all of the elements from the list.
  • Object set(int index, Object element): It is used to replace an existing element in the list with a new element.
  • void add(int index, Object element): It inserts the element at the position ‘index’ in the list.
  • void addFirst(Object element): It inserts the element at the beginning of the list.
  • void addLast(Object element): It appends the element at the end of the list.
  • Object get(int index): It returns the element at the position ‘index’ in the list. It throws ‘IndexOutOfBoundsException’ if the index is out of range of the list.
  • Object getFirst(): It returns the first element of the Linked List.
  • Object getLast(): It returns the last element of the Linked List.
  • int indexOf(Object element): If element is found, it returns the index of the first occurrence of the element. Else, it returns -1.
  • int lastIndexOf(Object element): If element is found, it returns the index of the last occurrence of the element. Else, it returns -1.
  • Object remove(): It is used to remove and return the element from the head of the list.
  • Object remove(int index): It removes the element at the position ‘index’ in this list. It throws ‘NoSuchElementException’ if the list is empty.
  • Object removeLast(): It is used to remove and return the last element of the Linked List.
Must Read: Java Tutorial

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Rajkumar SM is the founder of SoftwareTestingMaterial. He is a certified Software Test Engineer by profession and a blogger and YouTuber by choice. He has extensive experience in the field of Software Testing. Furthermore, he loves spending time with his wife and their cute little kid, 'Freedom.'

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