what does linked list add to tail code example

Example 1: linked list head and tail

import java.util.Iterator; 

// Custom Linked List class using Generics 
class List<T> implements Iterable<T> { 
	Node<T> head, tail; 
	
	// add new Element at tail of the linked list in O(1) 
	public void add(T data) 
	{ 
		Node<T> node = new Node<>(data, null); 
		if (head == null) 
			tail = head = node; 
		else { 
			tail.setNext(node); 
			tail = node; 
		} 
	} 
	
	// return Head 
	public Node<T> getHead() 
	{ 
		return head; 
	} 
	
	// return Tail 
	public Node<T> getTail() 
	{ 
		return tail; 
	} 
	
	// return Iterator instance 
	public Iterator<T> iterator() 
	{ 
		return new ListIterator<T>(this); 
	} 
} 

class ListIterator<T> implements Iterator<T> { 
	Node<T> current; 
	
	// initialize pointer to head of the list for iteration 
	public ListIterator(List<T> list) 
	{ 
		current = list.getHead(); 
	} 
	
	// returns false if next element does not exist 
	public boolean hasNext() 
	{ 
		return current != null; 
	} 
	
	// return current data and update pointer 
	public T next() 
	{ 
		T data = current.getData(); 
		current = current.getNext(); 
		return data; 
	} 
	
	// implement if needed 
	public void remove() 
	{ 
		throw new UnsupportedOperationException(); 
	} 
} 

// Constituent Node of Linked List 
class Node<T> { 
	T data; 
	Node<T> next; 
	public Node(T data, Node<T> next) 
	{ 
		this.data = data; 
		this.next = next; 
	} 
	
	// Setter getter methods for Data and Next Pointer 
	public void setData(T data) 
	{ 
		this.data = data; 
	} 
	
	public void setNext(Node<T> next) 
	{ 
		this.next = next; 
	} 
	
	public T getData() 
	{ 
		return data; 
	} 
	
	public Node<T> getNext() 
	{ 
		return next; 
	} 
} 

// Driver class 
class Main { 
	public static void main(String[] args) 
	{ 
		// Create Linked List 
		List<String> myList = new List<>(); 
		
		// Add Elements 
		myList.add("abc"); 
		myList.add("mno"); 
		myList.add("pqr"); 
		myList.add("xyz"); 
		
		// Iterate through the list using For Each Loop 
		for (String string : myList) 
			System.out.println(string); 
	} 
}

Example 2: adding an element to the end of a linked list java

class Node {
    Object data;
    Node next;
    Node(Object d,Node n) {
        data = d ;
        next = n ;
       }

   public static Node addLast(Node header, Object x) {
       // save the reference to the header so we can return it.
       Node ret = header;

       // check base case, header is null.
       if (header == null) {
           return new Node(x, null);
       }

       // loop until we find the end of the list
       while ((header.next != null)) {
           header = header.next;
       }

       // set the new node to the Object x, next will be null.
       header.next = new Node(x, null);
       return ret;
   }
}