Section 1 Summary

Great, the first section is complete, and now you have a grasp of the basics of the Java Collections Framework. You've learned how to work with wrapper classes, ArrayList, and LinkedList. We even wrote our simplified version of LinkedList, part of which you implemented yourself. Let's take a look at this implementation:

main


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package com.example;

class Node {
    int data;
    Node next;

    public Node(int data) {
        this.data = data;
        this.next = null;
    }
}

class SinglyLinkedList {
    private Node head;

    public SinglyLinkedList() {
        this.head = null;
    }

    public void append(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
            return;
        }

        Node current = head;
        while (current.next != null) {
            current = current.next;
        }

        current.next = newNode;
    }

    public void display() {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }

    public void update(int index, int newData) {
        if (index < 0 || index >= size()) {
            System.out.println("Invalid index");
            return;
        }

        Node current = head;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }

        current.data = newData;
    }

    public void delete(int index) {
        if (index < 0 || index >= size()) {
            System.out.println("Invalid Index");
            return;
        }

        if (index == 0) {
            head = head.next;
            return;
        }

        Node current = head;
        for (int i = 0; i < index - 1; i++) {
            current = current.next;
        }

        current.next = current.next.next;
    }

    public int size() {
        int count = 0;
        Node current = head;
        while (current != null) {
            count++;
            current = current.next;
        }
        return count;
    }

}

public class Main {
    public static void main(String[] args) {
        SinglyLinkedList linkedList = new SinglyLinkedList();

        // Adding elements to the end of the list (Create)
        linkedList.append(1);
        linkedList.append(2);
        linkedList.append(3);
        linkedList.append(4);

        // Displaying the content of the list (Read)
        System.out.println("Contents of the list:");
        linkedList.display();

        // Updating a value by index (Update)
        linkedList.update(2, 10);
        System.out.println("List after updating the value at index 2:");
        linkedList.display();

        // Deleting an element by index (Delete)
        linkedList.delete(1);
        System.out.println("List after deleting the element at index 1:");
        linkedList.display();
    }
}

Yes, the solution turned out to be quite large, so I understand the inconvenience of scrolling through the code in a small window. However, you can run this code and see how it works.

Here are the two methods that you implemented yourself:

SinglyLinkedList


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public void delete(int index) {
    if (index < 0 || index >= size()) {
        System.out.println("Invalid Index");
        return;
    }

    if (index == 0) {
        head = head.next;
        return;
    }
    Node current = head;
    for (int i = 0; i < index - 1; i++) {
        current = current.next;
    }

    current.next = current.next.next;
}

public int size() {
    int count = 0;
    Node current = head;
    while (current != null) {
        count++;
        current = current.next;
    }
    return count;
}

Your solution may differ slightly from the one I provided, but that's okay because programming is a creative process, and everyone's code can be completely different while serving the same functions.

Let's go over the main questions that were present in this section:

Everything was clear?

Thanks for your feedback!

Section 1. Chapter 8