gistfile1.java

import edu.princeton.cs.introcs.StdOut;
import java.util.Arrays;
import java.util.Iterator;

class ResizebleStack<Item> implements Iterable<Item> {
    private Item[] stack = (Item[]) new Object[1];
    private int N;

    public Item pop() {
        if (N > 0 && stack.length / 2 == N) {
            stack = Arrays.copyOf(stack, N);
        }
        N--;
        Item item = stack[N];
        stack[N] = null;
        return item;
    }

    public void push(Item item) {
        if (stack.length == N) {
            stack = Arrays.copyOf(stack, N * 2);
        }
        stack[N] = item;
        N++;
    }

    public Iterator<Item> iterator() {
        return new StackIterator();
    }

    private class StackIterator implements Iterator<Item> {
        private int i = N;

        public Item next() {
            return stack[--i];
        }

        public boolean hasNext() {
            return i > 0;
        }

        public void remove() {

        }
    }
}

class test {
    public static void main(String[] args) {
        ResizebleStack<Integer> stack = new ResizebleStack<Integer>();

        stack.push(2);
        stack.push(3);
        stack.push(4);

        for (Integer t : stack) {
            StdOut.print(t);
        }

        stack.pop();
        stack.pop();

        for (Integer t : stack) {
            StdOut.print(t);
        }
    }
}