generic Deque - Java Data Structure

Description

generic Deque
Demo Code

import java.util.Iterator;

public class Deque<Item> implements Iterable<Item> {
    private Node<Item> first;
    private Node<Item> last;

    // construct an empty deque
    public Deque() {

    }/*from  w  ww .jav a  2  s. c o m*/

    // is the deque empty?
    public boolean isEmpty() {
        return first == null;
    }

    // return the number of items on the deque
    public int size() {
        if (first == null)
            return 0;
        int itemcount = 1;
        Node<Item> current = first;
        while (current.next != null) {
            current = current.next;
            itemcount++;
        }
        return itemcount;
    }

    // insert the item at the front
    public void addFirst(Item item) {
        if (item == null)
            throw new NullPointerException();
        Node<Item> newnode = new Node<Item>();
        newnode.item = item;
        newnode.next = first;
        newnode.prev = null;
        if (first != null)
            first.prev = newnode;
        first = newnode;
        if (last == null)
            last = newnode;
    }

    // insert the item at the end
    public void addLast(Item item) {
        if (item == null)
            throw new NullPointerException();
        Node<Item> newnode = new Node<Item>();
        newnode.item = item;
        newnode.next = null;
        newnode.prev = last;
        if (last != null)
            last.next = newnode;
        last = newnode;
        if (first == null)
            first = newnode;
    }

    // delete and return the item at the front
    public Item removeFirst() {
        if (first == null)
            throw new java.util.NoSuchElementException();
        Item item = first.item;
        first = first.next;
        if (first != null)
            first.prev = null;
        else
            last = null;
        return item;
    }

    // delete and return the item at the end
    public Item removeLast() {
        if (last == null)
            throw new java.util.NoSuchElementException();
        Item item = last.item;
        last = last.prev;
        if (last != null)
            last.next = null;
        else
            first = null;
        return item;
    }

    // return an iterator over items in order from front to end
    public Iterator<Item> iterator() {
        return new DequeIterator();
    }

    private class DequeIterator implements Iterator<Item> {
        private Node<Item> current = first;

        public boolean hasNext() {
            return (current != null);
        }

        public void remove() {
            throw new UnsupportedOperationException();
        }

        public Item next() {
            if (current == null)
                throw new java.util.NoSuchElementException();
            Item item = current.item;
            current = current.next;
            return item;
        }
    }

    // item storage
    private class Node<Item> {
        private Item item;
        private Node<Item> next;
        private Node<Item> prev;
    }

    // unit testing
    public static void main(String[] args) {
        Deque<Integer> deque = new Deque<Integer>();
        // testing add/remove from start/end
        System.out
                .println("********** Testing Sequence Start @ First **********");
        for (int i = 1; i <= 5; i++) {
            deque.addFirst(i);
            deque.addLast(-i);
        }
        System.out.println("Expect 5 to -5");
        while (deque.size() > 0)
            System.out.print(String.format("%d ", deque.removeFirst()));
        System.out.println("");
        System.out
                .println("********** Testing Sequence Start @ Last **********");
        for (int i = 1; i <= 5; i++) {
            deque.addLast(-i);
            deque.addFirst(i);
        }
        System.out.println("Expect -5 to 5");
        while (deque.size() > 0)
            System.out.print(String.format("%d ", deque.removeLast()));
        System.out.println("");
        // testing iterator
        System.out
                .println("********** Testing ForEach Iterator **********");
        for (int i = 1; i <= 5; i++) {
            deque.addFirst(i);
            deque.addLast(-i);
        }
        System.out.println("Expect 5 to -5");
        for (int value : deque)
            System.out.print(String.format("%d ", value));
        // testing iterator
        System.out.println("");
        System.out
                .println("********** Testing Parralel Iterators **********");
        Iterator<Integer> iterator1 = deque.iterator();
        Iterator<Integer> iterator2 = deque.iterator();
        while (iterator1.hasNext())
            System.out.println(String.format("%1$d %2$d", iterator1.next(),
                    iterator2.next()));
        System.out.println("");
    }
}
generic Deque - Java Data Structure

Description

Demo Code

Related Tutorials
