import java.util.EmptyStackException;
public class Stack {
private ArrayList elementData = new ArrayList();
public void push(Object o){
elementData.add(o);
}
public Object pop(){
if(!isEmpty())
return elementData.remove();
else
throw new EmptyStackException();
}
public Object peek(){
int len = elementData.size();
if(!isEmpty())
return elementData.get(len-1);
throw new EmptyStackException();
}
public boolean isEmpty(){
if(elementData.size()==0)
return true;
else
return false;
}
public int size(){
return elementData.size();
}
/* public static void main(String[] args){
Stack s = new Stack();
s.push("123");
s.push("1");
s.push("1234");
s.push("1253");
s.push("1263");
System.out.println(s.size());
System.out.println(s.peek());
System.out.println(s.pop());
System.out.println(s.isEmpty());
}*/
}