Last Updated on December 13, 2022 by Prepbytes
Introduction
One of the most crucial data structures to learn while preparing for interviews is the linked list. In a coding interview, having a thorough understanding of LinkedList might be a significant benefit.
In this article, we will see how to iterate a linked list in java.
Ways to iterate LinkedList in java
1) Using loop:
- for loop
- while loop
- do while loop
2) Using enhanced for loop.
3) Using forEach() method.
4) Using iterators - iterator() method
- listIterator() method
5) Using isEmpty() and poll() method
6) Using streams.
Approach 1
Using for loop
The below program shows how to iterate a linked list in java using for loop.
Code Implementation:
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<Integer> list = new LinkedList<Integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using for loop
System.out.print("Iterating the linked list using for loop : ");
for(int i = 0 ;i<list.size();i++) {
System.out.print(list.get(i) + " ");
}
}
}
Output
Iterating the linked list using for loop : 1 2 3 4 9 11
Time Complexity: O(n), as we are traversing the list, and n is the number of nodes in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used.
Approach 2
Using while loop
The below program shows how to iterate a linked list in java using while loop.
Code Implementation
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using while loop
System.out.print("Iterating the linked list using while loop : ");
int i = 0;
while(i < list.size()) {
System.out.print(list.get(i) + " ");
i++;
}
}
}
Output
Iterating the linked list using while loop : 1 2 3 4 9 11
Time Complexity: O(n), as we are traversing the list, and n is the number of nodes in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used.
Approach 3
Using do while loop
The below program shows how to iterate a linked list in java using do while loop.
Code Implementation
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList list = new LinkedList();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using do while loop
System.out.print("Iterating the linked list using do while loop : ");
int i = 0;
do {
System.out.print(list.get(i) + " ");
i++;
}
while(i < list.size());
}
}
Output
Iterating the linked list using do while loop : 1 2 3 4 9 11
Time Complexity: O(n), as we are traversing the list, and n is the number of nodes in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used.
Approach 4
Using enhanced for loop
The below program shows how to iterate a linked list in java using enhanced for loop.
Code Implementation
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using Enhanced for loop
System.out.print("Iterating the linked list using enhanced for loop : ");
for(Integer element : list) {
System.out.print(element + " ");
}
}
}
Output
Iterating the linked list using enhanced for loop : 1 2 3 4 9 11
Time Complexity: O(n), as we are traversing the list, and n is the number of nodes in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used.
Approach 5
Using forEach() method
The below program shows how to iterate a linked list in java using forEach() method.
Syntax:
forEach(Consumer action)
Return value
void
Code Implementation
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using forEach loop
System.out.print("Iterating the linked list using forEach() method : ");
list.forEach((element) -> System.out.print(element + " "));
}
}
Output
Iterating the linked list using forEach() method : 1 2 3 4 9 11
Time Complexity: O(n), as we are traversing the list and n is the number of nodes in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used because forEach internally iterates over the elements of collections.
Approach 6
Using Iterator() method
The below program shows how to iterate a linked list in java using iterator() method.
Syntax
LinkedList.iterator()
Return value
The LinkedList.iterator() method returns an iterator over the sequence of elements of the Linked List in proper order.
Code Implementation
import java.util.LinkedList;
import java.util.Iterator;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using iterator
System.out.print("Iterating the linked list using iterator : ");
Iterator<integer> itr = list.iterator();
while(itr.hasNext()) {
System.out.print(itr.next()+ " ");
}
}
}
Output
Iterating the linked list using iterator : 1 2 3 4 9 11
Time Complexity: O(n), where n is the number of elements in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used because iterator() creates an iterator over the elements of the list.
Approach 7
Using listIterator() method
The below program shows how to iterate a linked list in java using listIterator() method.
Syntax
LinkedList.listIterator()
Return value
The LinkedList.listIterator() method returns a list iterator over the sequence of elements of the Linked List in proper order.
Code Implementation
import java.util.LinkedList;
import java.util.Iterator;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList list = new LinkedList();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
// Iterate using iterator
System.out.print("Iterating the linked list using listIterator() method : ");
Iterator itr = list.listIterator();
while(itr.hasNext()) {
System.out.print(itr.next()+ " ");
}
}
}
Output
Iterating the linked list using listIterator() method : 1 2 3 4 9 11
Time Complexity: O(n), where n is the number of elements in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used because listIterator() creates a list iterator over the elements of the list.
Approach 8
Using isEmpty() and poll() methods
The below program shows how to iterate a linked list in java using isEmpty() and poll() method.
Syntax
-
LinkedList.isEmpty()
-
LinkedList.poll()
Return value
-
isEmpty() method returns true if this list is empty, false otherwise.
-
poll() method retrieves and removes the head of this list.
Code Implementation
import java.util.LinkedList;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
System.out.print("Iterating the linked list using isEmpty() and poll() method : ");
while(!list.isEmpty()) {
System.out.print(list.poll()+ " ");
}
}
}
Output
Iterating the linked list using isEmpty() and poll() method : 1 2 3 4 9 11
Time Complexity: O(n), where n is the number of elements in the linked list.
Space Complexity: O(1), Constant auxiliary space is being used.
Approach 9
Using streams
The below program shows how to iterate a linked list in java using streams.
Code Implementation
import java.util.LinkedList;
import java.util.stream.Stream;
public class Prepbytes {
public static void main(String[] args) {
/*
* Create an empty LinkedList
*/
LinkedList<integer> list = new LinkedList<integer>();
// Add values to the list
list.add(1);
list.add(2);
list.add(3);
list.add(4);
list.add(9);
list.add(11);
Stream<integer> stream = list.stream();
System.out.print("Iterating the linked list using streams : ");
stream.forEach(s -> System.out.print(s+" "));
}
}
Output
Iterating the linked list using streams : 1 2 3 4 9 11
Time Complexity: O(n), where n is the number of elements in the linked list.
[forminator_quiz id=”5382″]
So, in this blog, we have learned different ways to iterate a LinkedList in java. If you want to practice questions on linked list, feel free to solve them at Prepbytes (Linked List).