Stack.java

package com.coding.weak1;

import java.util.ArrayList;
import java.util.NoSuchElementException;

public class Stack {
	private ArrayList elementData = new ArrayList();
	
	public void push(Object o){
		elementData.add(o);
	}
	
	public Object pop(){
		if(isEmpty()){
			throw new NoSuchElementException();
		}
		return elementData.remove(elementData.size() - 1);
	}
	
	public Object peek(){
		if (size() == 0)
			return null;
		return elementData.get(elementData.size()-1);
	}
	public boolean isEmpty(){
		return elementData.size() == 0;
	}

	public int size(){
		return elementData.size();
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		if (isEmpty()) {
			return "";
		}
		for (int i = elementData.size() - 1; i >= 0; i--) {
			sb.append(elementData.get(i).toString());
			sb.append(",");
		}
		return sb.substring(0, sb.lastIndexOf(","));
	}
}