Single Linked List

public class MySingleLinkedList {
    Element head;
    Element tail;

    public MySingleLinkedList(){
        this.head = null;
        this.tail = null;
    }

    public void append(Element e){
        if (this.head == null){
            this.head = e;
        }
        else{
            this.tail.next = e;
        }
        this.tail = e;
    }

    public void prepend(Element e){
        if (this.head == null){
            this.tail = e;
        }
        else{
            e.next = this.head;
        }
        this.head = e;
    }

    public void insertBefore(Element e, int n){
        int counter = 0;
        Element previous = head;
        Element current = head.next;

        while (counter+1 < n){
            previous = current;
            current = current.next;
            counter++;
        }
        e.next = current;
        previous.next = e;
    }

    public void insertAfter(Element e, int n){
        int counter = 0;
        Element previous = this.head;
        Element current = this.head.next;

        while (counter < n){
            previous = current;
            current = current.next;
            counter++;
        }
        e.next = current;
        previous.next = e;
    }

    public void extractFirst(){
        if(this.head == null){
            System.out.println("Error");
        }
        this.head = this.head.next;
        if(this.head == null){
            System.out.println("Error");
        }
    }

    public void extractLast(){
        if (this.tail == null){
            System.out.println("Error");
        }
        if (this.head == this.tail){
            this.head = this.tail = null;
        }
        else{
            Element previous = this.head;
            while(previous.next != null){
                previous = previous.next;
            }
            previous.next = null;
            this.tail = previous;
        }
    }

    public int countNodes(){
        int counter = 0;
        Element first = this.head;
        while(first != null){
            counter++;
            first = first.next;
        }
        return counter;
    }

    public int searchNode(Object obj){
        int counter = 0;
        Element first = this.head;
        while(first != null){
            if (first.data.equals(obj)){
                counter++;
            }
            first = first.next;
        }
        return counter;
    }

    public void display(){
        Element start = this.head;
        while (start != null){
            start.print();
            start = start.next;
        }
    }
}