Thread: About add and remove method of ListNode, i don't understand....

class ListNode {
	private	Object data;
	private	ListNode next;
	ListNode(Object o) { data = o; next = null; }
	ListNode(Object o, ListNode nextNode) 
		{ data = o; next = nextNode; }
	void setData(Object data){
		this.data = data;
	}
	void setNext(ListNode next){
		this.next = next;
	}
	Object getData() { return data; }
	ListNode getNext() { return next; }
} // class ListNode
 
class EmptyListException extends RuntimeException {
	public EmptyListException () { super ("List is empty"); }
} // class EmptyListException
 
class LinkedList {
	private ListNode head;
	private ListNode tail;
	public LinkedList() { head = tail = null; }
 
	public boolean isEmpty() { return head == null; }
 
	public void addToHead(Object item) {
		if (isEmpty())
			head = tail = new ListNode(item);
		else
			head = new ListNode(item,head);
	}
	public void addToTail(Object item) {
		if (isEmpty())
			head = tail = new ListNode(item);
		else{
			tail.setNext(new ListNode(item));
			tail = tail.getNext();
		}
	}
	public Object removeFromHead() throws EmptyListException {
		Object item = null;
		if (isEmpty())
			throw new EmptyListException();
		item = head.getData();
		if ( head == tail )
			head = tail = null;
		else
			head = head.getNext();
		return item;
	}
	public Object removeFromTail() throws EmptyListException {
		Object item = null;
		if (isEmpty())
			throw new EmptyListException();
		item = tail.getData();
		if (head == tail)
			head = tail = null;
		else{
			ListNode current = head;
			while(current.getNext() != tail){
				current = current.getNext();
			}
			tail = current;
			current.setNext(null);
		}
		return item;
	}
	@Override
	public String toString () {
		String s = "[ ";
		ListNode current = head;
		while (current != null) {
			s += current.getData() + " ";
			current = current.getNext();
		}
		return s + "]";
	}
 
	public int count(){
		if (isEmpty())
			return 0;
		int count = 0;
		ListNode current = head;
		while (current != null){
			count++;
			current = current.getNext();
		}
		return count;
	}
 
	public Object get(int n){
		ListNode current = head;
		if (n >= 1 && n <= count()){
			for (int i = 1; i < n; i++){
				current = current.getNext();
			}
			return current.getData();
		}
		else{
			return null;
		}
	}
 
	public Object remove(int n){
		if (n < 1 || n > count())
			return null;
		ListNode current = head;
		ListNode previous = head;
		while (!current.getData().equals(get(n))){
			current = current.getNext();
		}
		if ( n == 1){
			removeFromHead();
		}
		else if (n == count()){
			removeFromTail();
		}
		else{
			while (!previous.getData().equals(get(n-1))){
				previous = previous.getNext();
			}
			previous.setNext(current.getNext());
		}
		return current.getData();
	}
 
	public void add(int n, Object item){
		ListNode current = head;
		ListNode previous = head;
		if (n <= 1){
			addToHead(item);
		}
		else if (n > count()){
			addToTail(item);
		}
		else{
			while (!current.getData().equals(get(n))){
				current = current.getNext();
			}
			while (!previous.getData().equals(get(n-1))){
				previous = previous.getNext();
			}
			previous.setNext(new ListNode(item, current));
		}
	}
} // class LinkedList

Who can explain the logic of method?
Thank you

Have you tried playing computer with the code using a piece of paper to see what it does?