LinkedList

public class LinkedList {

    private static class Node {
        int data;
        Node next;

        public Node(int data){
            this.data = data;
        }

        public Node(int data, Node next){
            this.data = data;
            this.next = next;
        }
    }

    private Node head, tail;
    private int count = 0;

    public int size(){
        return count;
    }
    
    // If the LL is empty, create a new node,
    // that new node is head and tail.
    // If LL is not empty, prepend as before. 
    public void prepend(int d){
        if (head == null)
            tail = head = new Node(d);
        else 
            head = new Node(d, head);
        count++;
    }

    public void append(int d){
        if (head == null)
            tail = head = new Node(d);
        else
            tail = tail.next = new Node(d);
        count++;
    }
    
    public boolean contains(int d){
        Node curr = head;
        while (curr != null && curr.data != d)
            curr = curr.next;
        return curr != null;
    }
    
    public int get(int idx){
        if (idx >= count || idx < 0) throw new IndexOutOfBoundsException();
        Node curr = head;
        for (int i = 0; i < idx; i++){
            curr = curr.next;
        }
        return curr.data;
    }

    // Insert d into the linked list at index idx
    // Find the node *before* where the new node is
    // to be inserted. Create the new node and update
    // references as necessary. 
    public void insert(int idx, int d){
        if (idx > count || idx < 0) throw new IndexOutOfBoundsException();
        if (idx == 0)
            prepend(d);
        else {
            Node curr = head;
            for (int i = 0; i < idx-1; i++){
                curr = curr.next;
            }
            Node newNode = new Node(d, curr.next);
            curr.next = newNode;
        }
        count++;
    }
    
    @Override
    public String toString(){
        String retVal = "Linked list of size: " + count + '\n';

        for (Node temp = head; temp != null; temp = temp.next)
            retVal += temp.data + " ";

        
        /*Node curr = head;
        while(curr != null){
            retVal += curr.data + " ";
            curr = curr.next;
            }*/
        return retVal;
    }

    
    // Testing our LL:
    public static void main(String[] args){
        LinkedList ll = new LinkedList();
        ll.prepend(10);
        ll.prepend(45);
        ll.prepend(23);
        System.out.println("Contains 45? " + ll.contains(45));
        System.out.println("Contains 37? " + ll.contains(37));
        System.out.println(ll);
        ll.append(19);
        System.out.println(ll);
        System.out.println("First element: " + ll.get(0));
        System.out.println("Last element: " + ll.get(3));
        //      System.out.println("Last element: " + ll.get(4));
        ll.insert(4, 15);
        System.out.println(ll);
    }
}