How to Implement Linked List in Java | Insertion & Deletion Explained

Mastering Linked Lists in Java: A Step-by-Step Implementation (Singly Linked List)

In this tutorial, we’ll implement a Singly Linked List in Java. The code includes detailed comments to explain what each part does.

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Node Class

// Node represents each element in the Linked List
public class Node {
    int data;     // Stores the value
    Node next;    // Points to the next node

    // Constructor initializes data and sets next to null
    public Node(int data) {
        this.data = data;
        this.next = null;
    }
}

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LinkedList Class

// LinkedList class manages all operations
public class LinkedList {
    Node head;  // The first node in the list

    // Constructor initializes the head as null (empty list)
    public LinkedList() {
        this.head = null;
    }

    // Check if the list is empty
    public boolean isEmpty() {
        return this.head == null;
    }

    // Insert a node at the beginning
    public void insertAtBeginning(int data) {
        Node newNode = new Node(data);   // Create a new node
        if (isEmpty()) {
            this.head = newNode;         // If empty, new node becomes head
        } else {
            newNode.next = this.head;    // Link new node to current head
            this.head = newNode;         // Update head to new node
        }
    }

    // Insert a node at the end
    public void insertAtEnd(int data) {
        Node newNode = new Node(data);   // Create a new node
        if (isEmpty()) {
            this.head = newNode;         // If list empty, new node is head
        } else {
            Node temp = this.head;       // Start from head
            while (temp.next != null) {  // Traverse till last node
                temp = temp.next;
            }
            temp.next = newNode;         // Attach new node at the end
        }
    }

    // Insert a node after a given value
    public void insertAtPosition(int data, int checkedValue) {
        Node newNode = new Node(data);   // Create a new node
        if (isEmpty()) {
            this.head = newNode;         // If empty, new node is head
        } else {
            Node temp = this.head;
            while (temp != null) {
                if (temp.data == checkedValue) {   // Found the target value
                    newNode.next = temp.next;      // Link new node to next
                    temp.next = newNode;           // Insert after target node
                    break;
                }
                temp = temp.next;   // Move to next node
            }
        }
    }

    // Print the Linked List
    public void printList() {
        if (isEmpty()) {
            System.out.println("Linked List is Empty");
        } else {
            Node temp = this.head;
            while (temp != null) {    // Traverse all nodes
                System.out.print(temp.data + " "); // Print data
                temp = temp.next;     // Move to next node
            }
            System.out.println();
        }
    }

    // Delete the first node
    public void deleteFromBeginning() {
        if (!isEmpty()) {
            this.head = this.head.next;  // Head moves to next node
        }
    }

    // Delete the last node
    public void deleteFromEnd() {
        if (!isEmpty()) {
            if (this.head.next == null) {
                this.head = null;       // Only one node -> make list empty
            } else {
                Node temp = this.head;
                while (temp.next.next != null) {  // Find 2nd last node
                    temp = temp.next;
                }
                temp.next = null;   // Remove link to last node
            }
        }
    }

    // Delete a specific node by value
    public void deleteFromSpecificPosition(int deleted) {
        if (!isEmpty()) {
            if (this.head.data == deleted) {  // If head node matches
                this.head = this.head.next;
                return;
            }
            Node temp = this.head;
            Node prev = null;
            while (temp != null) {
                if (temp.data == deleted) {   // Found node to delete
                    prev.next = temp.next;    // Bypass the node
                    return;
                }
                prev = temp;       // Store previous node
                temp = temp.next;  // Move forward
            }
        }
    }
}

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Main Class – Testing the Linked List

// Main class to test LinkedList operations
public class Main {
    public static void main(String[] args) {
        LinkedList myList = new LinkedList();

        // Insert nodes at beginning and end
        myList.insertAtBeginning(10);
        myList.insertAtEnd(20);
        myList.insertAtBeginning(30);
        myList.insertAtEnd(40);
        myList.printList();  // Output: 30 10 20 40

        // Insert one more node at beginning
        myList.insertAtBeginning(5);
        myList.printList();  // Output: 5 30 10 20 40

        // Insert 35 after node with value 30
        myList.insertAtPosition(35, 30);
        myList.printList();  // Output: 5 30 35 10 20 40

        // Delete first node
        myList.deleteFromBeginning();
        myList.printList();  // Output: 30 35 10 20 40

        // Delete last node
        myList.deleteFromEnd();
        myList.printList();  // Output: 30 35 10 20

        // Delete node with value 20
        myList.deleteFromSpecificPosition(20);
        myList.printList();  // Output: 30 35 10
    }
}

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Final Output

30 10 20 40
5 30 10 20 40
5 30 35 10 20 40
30 35 10 20 40
30 35 10 20
30 35 10

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Conclusion

With comments explaining each step, it’s easier to understand how a Singly Linked List works internally. By practicing insertions, deletions, and traversals, you’ll strengthen your foundation in Data Structures, which is essential for advanced topics like stacks, queues, and graphs.