programming-examples/java/Basics/Program to Reverse Singly Linked List (Java).java

/*
Recursive Method:
    1) Divide the list in two parts - first node and rest of the linked list.
    2) Call reverse for the rest of the linked list.
    3) Link rest to first.
    4) Fix head pointer.
    */


public class SinglyLinkedListImpl<T>
{

    private Node<T> head;

    public void add(T element)
    {
        Node<T> nd = new Node<T>();
        nd.setValue(element);
        System.out.println("Adding: "+element);
        Node<T> tmp = head;
        while(true)
            {
                if(tmp == null)
                    {
                        //since there is only one element, both head and
                        //tail points to the same object.
                        head = nd;
                        break;
                    }
                else if(tmp.getNextRef() == null)
                    {
                        tmp.setNextRef(nd);
                        break;
                    }
                else
                    {
                        tmp = tmp.getNextRef();
                    }
            }
    }

    public void traverse()
    {
        Node<T> tmp = head;
        while(true)
            {
                if(tmp == null)
                    {
                        break;
                    }
                System.out.print(tmp.getValue()+"\t");
                tmp = tmp.getNextRef();
            }
    }

    public void reverse()
    {
        System.out.println("\nreversing the linked list\n");
        Node<T> prev = null;
        Node<T> current = head;
        Node<T> next = null;
        while(current != null)
            {
                next = current.getNextRef();
                current.setNextRef(prev);
                prev = current;
                current = next;
            }
        head = prev;
    }

    public static void main(String a[])
    {
        SinglyLinkedListImpl<Integer> sl = new SinglyLinkedListImpl<Integer>();
        sl.add(3);
        sl.add(32);
        sl.add(54);
        sl.add(89);
        System.out.println();
        sl.traverse();
        System.out.println();
        sl.reverse();
        sl.traverse();
    }
}

class Node<T> implements Comparable<T>
{

    private T value;
    private Node<T> nextRef;

    public T getValue()
    {
        return value;
    }
    public void setValue(T value)
    {
        this.value = value;
    }
    public Node<T> getNextRef()
    {
        return nextRef;
    }
    public void setNextRef(Node<T> ref)
    {
        this.nextRef = ref;
    }
    @Override
    public int compareTo(T arg)
    {
        if(arg == this.value)
            {
                return 0;
            }
        else
            {
                return 1;
            }
    }
}