SLList

public class ControlFlow {
   public static void main(String[] args) {
        /* Creates a list of one Interger, namely 10 */
        SLList L = new SLList();

        L.addLast(20);
        L.addFirst(23);
        L.addFirst(12);
        L.displayList();
    }

}


public class SLList {
    public static class IntNode {
        public int item;
        public IntNode next;

        public IntNode(int i, IntNode n) {
            item = i;
            next = n;
        }
        public void displayNode(){
            System.out.println("{ "+ item + " } ");
        }
    }

    private IntNode sentinel;
    private int size;

    public SLList() {
        sentinel = new IntNode(63,null);

        size = 0;
    }

    public SLList(int x) {
        sentinel = new IntNode(63,null);
        sentinel.next = new IntNode(x,null);

        size += 1;
    }

    /**
     * Adds an item to the front of the list.
     */
    public void addFirst(int x) {
        sentinel.next=new IntNode(x,sentinel.next);
        size += 1;

    }

    /**
     * Retrieves the front item from the list.
     */
    public int getFirst() {
        return sentinel.next.item;
    }

    /**
     * Adds an item to the end of the list.
     */
    public void addLast(int x) {
        size += 1;
        IntNode p = sentinel;

        while (p.next != null) {
            p = p.next;
        }
        p.next = new IntNode(x, null);


    }

    public int size3() {
        return size;
    }

    /**
     * Returns the number of items in the list using recursion.
     */
    public int size() {
        IntNode p = sentinel;
        int count = 1;

        while (p.next != null) {
            p = p.next;
            count++;
        }

        return count;
    }

    public static int size2(IntNode p) {
        if (p.next == null) {
            return 1;
        }
        return 1 + size2(p.next);

    }

    public int size2() {
        return size2(sentinel);

    }

    public void displayList(){
        System.out.println("List (first --> last) ");
        IntNode current = sentinel;
        while(current != null){
            current.displayNode();
            current = current.next;
        }
        System.out.println();
    }