GTestStack.java

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

class Stack<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 int count = 0;

public void push(T obj) {
        Node<T> newnode = new Node<T>(obj);
        newnode.next = head;
        head = 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 pop() {
        if (head == null) return null;
        else {
            T data = head.data;
            head = head.next;
            count--;
            return data;
        }
    }
   
    public void clear() {
        while (!isEmpty()) pop();
    }
    
    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 GTestStack {
    public static void main(String[] args) {
        Stack<String> stk = new Stack<String>();
        stk.push(new String("Item 1"));
        stk.push(new String("Item 2"));
        stk.push(new String("Item 3"));
        stk.push(new String("Item 4"));
        System.out.println(stk);
        System.out.println(stk.length());
        System.out.println(stk.peek());
        while (!stk.isEmpty()) {
            System.out.println("Removed: " + stk.pop());
        }
        System.out.println(stk.length());
    }
}