GTestQueue.java

/*
    GTestQueue.java
    Dave Klick
    2014-03-26
    
    Queue implementation that accepts any type of object.
*/

class Queue<T> {
    private class Node<T> {
        T data;
        Node<T> next;
       
        public Node(T obj) {
            data = obj;
            next = null;
        }
      
        public Node(Node<T> n) {
            data = n.data;
            next = null;
        }
    }

private Node<T> head = null;
    private Node<T> tail = null;
    private int count = 0;

public void add(T obj) {
        Node<T> newnode = new Node<T>(obj);
        if (tail == null) {
            head = tail = newnode;
        } else {
            tail.next = newnode;
            tail = newnode;
        }
        count++;
    }
    
    public boolean isEmpty() { return head==null; }
    
    public int length() { return count; }
    public int size() { return count; }

public T peek() {
        if (head == null) return null;
        else return head.data;      
    }
    
    public T remove() {
        if (head == null) return null;
        else {
            T data = head.data;
            head = head.next;
            if (head == null) tail = null;
            count--;
            return data;
        }
    }
    
    public void clear() {
        while (!isEmpty()) remove();
    }
    
    public String toString() {
        StringBuilder s = new StringBuilder();
        Node<T> cur = head;
        while (cur != null) {
            if (s.length() > 0) s.append(", ");
            s.append(cur.data.toString());
            cur = cur.next;
        }
        return s.toString();
    }
}

public class GTestQueue {
    public static void main(String[] args) {
        Queue<String> q = new Queue<String>();
        q.add(new String("Item 1"));
        q.add(new String("Item 2"));
        q.add(new String("Item 3"));
        q.add(new String("Item 4"));
        System.out.println(q);
        System.out.println(q.length());
        System.out.println(q.peek());
        while (!q.isEmpty()) {
            System.out.println("Removed: " + q.remove());
        }
        System.out.println(q.length());
    }
}