package stackImplementation;

public class Stack {

	// The maximum possible size of a stack.
	public static final int MaxSize = 100;

	// The array index of the last active element
	// in the stack. A value of -1 means the stack
	// is currently empty.
	private int top = -1;

	// The stack elements, stored in an array.
	private Object[] store = new Object[MaxSize];

	// Number of all pushes (collectively)
	// done to all stacks.
	private static int totalNumberOfPushes = 0;

	// Add a new element at the top of the stack
	// (if there’s space left).
	public void push(Object newItem) {
		if (top < MaxSize - 1) {
			top++;
			store[top] = newItem;
			totalNumberOfPushes++;
		} else {
			System.out.println("Sorry, stack full.");
		}
	}

	// Remove the top element of the stack and return
	// it; check that the stack has elements in it!
	public Object pop() {
		Object ans = "";
		if (top >= 0) {
			ans = store[top];
			top--;
		} else {
			System.out.println("Sorry, stack empty.");
		}
		return ans;
	}

	// Return the number of elements that are
	// currently in the stack.
	public int size() {
		return top + 1;
	}

	// Return the total number of pushes
	// done to all stacks (collectively).
	public static int getNumberOfPushes() {
		return totalNumberOfPushes;
	}

	// Print the stack from top to bottom.
	// (not a standard function of stacks!)
	public void print() {
		int i;
		for (i = top; i >= 0; i--) {
			System.out.println(store[i]);
		}
	}

	// =============================================================
	// Below are the 2 new methods that the students need to define:
	// =============================================================

	// Return the top element of the stack without removing
	// it; check that the stack has elements in it!
	public Object peek() {
		Object ans = "";
		if (top >= 0) {
			ans = store[top];
		} else {
			System.out.println("Sorry, stack empty.");
		}
		return ans;
	}

	// Check if the stack has no elements in it -- return
	// true if the stack is empty, otherwise return false.
	public boolean isEmpty() {
		if (top >= 0) {
			return false;
		} else {
			return true;
		}
	}

}