Java class with generic data types

Question

I am trying to write a simple linked list class that uses generic data type. I am new to Java so I can't figure out how to debug the error message in the main method that arises when I try to insert data into an instance of my class. The class code and the main method are as follows:

import java.io.*; 
  
// Java program to implement 
// a Singly Linked List 
public class MyLinkedList<T> {
    

     Node head; // head of the list
     class Node<T> {
    
     T data;
     Node next;
     // Constructor
         Node(T d)
         {
             data = d;
             next = null;
         }
         }
      
        // Method to insert a new node 
    MyLinkedList insert(MyLinkedList list, T data)
    { 
        // Create a new node with given data 
            Node new_node = new Node(data); 
            new_node.next = null; 
      
            // If the Linked List is empty, 
        // then make the new node as head 
        if (list.head == null) { 
            list.head = new_node; 
        } 
        else { 
            // Else traverse till the last node 
            // and insert the new_node there 
                Node last = list.head; 
                while (last.next != null) { 
                    last = last.next; 
                } 
      
                // Insert the new_node at last node 
                last.next = new_node; 
            } 
      
            // Return the list by head 
        return list; 
    }    
    // Driver code 
    public static void main(String[] args) 
    { 
        /* Start with the empty list. */
        MyLinkedList list = new MyLinkedList();
        
        // Insert the values 
        list = insert(list, 1);
    } 
}

Answer 1

1. You need to change int to T in class declaration and method signature.

    class MyLinkedList<T> {
    MyLinkedList() {
    head=null;
    }
    Node head; // head of list
    class Node<T> {
   
    T data;
    Node next;
   
    // Constructor
    Node(T d) {
        data = d;
        next = null;
    }
   

   }

   // Method to insert a new node

   public void insert(T data) {
    // Create a new node with given data
    Node new_node = new Node(data);
    new_node.next = null;
   
    // If the Linked List is empty,
    // then make the new node as head
    if (this.head == null) {
        this.head = new_node;
    } else {
        Node last = this.head;
        while (last.next != null) {
            last = last.next;
        }
        // Insert the new_node at last node
        last.next = new_node;
    }
   

   }

    protected void display() {
    Node myNode=head;
    System.out.println();
    while (myNode != null) {
        System.out.println(myNode.data);
        myNode=myNode.next;
    }
   

   }

2. Change the insert method signature to the below:

   public static void main(String[] args) {
    /* Start with the empty list. */
    MyLinkedList<Integer> list = new MyLinkedList<Integer>();
   
    // Insert the values
    list.insert(1);
    list.insert(3);
    list.insert(12);
    list.insert(11);
    list.insert(21);
    list.insert(22);
    list.insert(45);
    list.display();
    }
   

3. For clear coding and understanding I have changed class name as MyLinkedList