ArrayBasedStacks.java

/*
 * 
 * This code is written for Stacks tutorial
 * The comment won't make sense unless you read the slide that goes with it
 * 
 * Go to Vumari.com to find the slide
 * 
 */

import java.util.Arrays;

public class ArrayBasedStacks {
	
	private Integer stacks[];
	private int index = 0;
	
	public ArrayBasedStacks(int size){
		stacks = new Integer[size];
	}
	
	public void push(int data){
	
		if(index == stacks.length){
			//you can either resize here or throw exception
			throw new ArrayIndexOutOfBoundsException("Stack is already full");
		}
		//add item to current index & increase index by 1;
		stacks[index++] = data;
	}
	
	public int pop(){
		
		if(isEmpty()){
			throw new NullPointerException("There is nothing to pop from the stack.");
		}
		int temp = stacks[--index];
		stacks[index] = null;
		return temp;		
	}
	
	public int getSize(){
		//index is 0 based but our index always points to next empty location
		//that will compensate for 0 & return exact size
		return index;
	}
	
	public boolean isEmpty(){
		return index == 0;
	}
	
	@Override
	public String toString() {
		StringBuilder stackData = new StringBuilder(Arrays.deepToString(stacks));
		return stackData.reverse().toString();
	}
}