Another Commit

doubly_linked_list.java

@@ -0,0 +1,133 @@
+import java.util.NoSuchElementException;
+
+public class DoublyLinkedListImpl<E> {
+
+    private Node head;
+    private Node tail;
+    private int size;
+
+    public DoublyLinkedListImpl() {
+        size = 0;
+    }
+    /**
+     * this class keeps track of each element information
+     * @author java2novice
+     *
+     */
+    private class Node {
+        E element;
+        Node next;
+        Node prev;
+
+        public Node(E element, Node next, Node prev) {
+            this.element = element;
+            this.next = next;
+            this.prev = prev;
+        }
+    }
+    /**
+     * returns the size of the linked list
+     * @return
+     */
+    public int size() { return size; }
+
+    /**
+     * return whether the list is empty or not
+     * @return
+     */
+    public boolean isEmpty() { return size == 0; }
+
+    /**
+     * adds element at the starting of the linked list
+     * @param element
+     */
+    public void addFirst(E element) {
+        Node tmp = new Node(element, head, null);
+        if(head != null ) {head.prev = tmp;}
+        head = tmp;
+        if(tail == null) { tail = tmp;}
+        size++;
+        System.out.println("adding: "+element);
+    }
+
+    /**
+     * adds element at the end of the linked list
+     * @param element
+     */
+    public void addLast(E element) {
+
+        Node tmp = new Node(element, null, tail);
+        if(tail != null) {tail.next = tmp;}
+        tail = tmp;
+        if(head == null) { head = tmp;}
+        size++;
+        System.out.println("adding: "+element);
+    }
+
+    /**
+     * this method walks forward through the linked list
+     */
+    public void iterateForward(){
+
+        System.out.println("iterating forward..");
+        Node tmp = head;
+        while(tmp != null){
+            System.out.println(tmp.element);
+            tmp = tmp.next;
+        }
+    }
+
+    /**
+     * this method walks backward through the linked list
+     */
+    public void iterateBackward(){
+
+        System.out.println("iterating backword..");
+        Node tmp = tail;
+        while(tmp != null){
+            System.out.println(tmp.element);
+            tmp = tmp.prev;
+        }
+    }
+
+    /**
+     * this method removes element from the start of the linked list
+     * @return
+     */
+    public E removeFirst() {
+        if (size == 0) throw new NoSuchElementException();
+        Node tmp = head;
+        head = head.next;
+        head.prev = null;
+        size--;
+        System.out.println("deleted: "+tmp.element);
+        return tmp.element;
+    }
+
+    /**
+     * this method removes element from the end of the linked list
+     * @return
+     */
+    public E removeLast() {
+        if (size == 0) throw new NoSuchElementException();
+        Node tmp = tail;
+        tail = tail.prev;
+        tail.next = null;
+        size--;
+        System.out.println("deleted: "+tmp.element);
+        return tmp.element;
+    }
+
+    public static void main(String a[]){
+
+        DoublyLinkedListImpl<Integer> dll = new DoublyLinkedListImpl<Integer>();
+        dll.addFirst(10);
+        dll.addFirst(34);
+        dll.addLast(56);
+        dll.addLast(364);
+        dll.iterateForward();
+        dll.removeFirst();
+        dll.removeLast();
+        dll.iterateBackward();
+    }
+}