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