what is in the head and tail of a linked list code example

Example: linked list head and tail

import java.util.Iterator; 

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

class ListIterator implements Iterator { 
	Node current; 
	
	// initialize pointer to head of the list for iteration 
	public ListIterator(List 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 data; 
	Node next; 
	public Node(T data, Node 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 next) 
	{ 
		this.next = next; 
	} 
	
	public T getData() 
	{ 
		return data; 
	} 
	
	public Node getNext() 
	{ 
		return next; 
	} 
} 

// Driver class 
class Main { 
	public static void main(String[] args) 
	{ 
		// Create Linked List 
		List 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); 
	} 
}