import java.util.EmptyStackException;
/**
* Created by fantasy on 2017-03-13.
*/
public class Stack {
private ArrayList elementData = new ArrayList();
public void push(Object o){
elementData.add(o);
}
public Object pop(){
if(elementData.size() == 0)
{
return elementData.remove(elementData.size() - 1 );
}
return null;
}
public Object peek(){
if(elementData.size() == 0 )
{
return elementData.get(elementData.size() - 1);
}
throw new EmptyStackException();
}
public boolean isEmpty(){
return !(elementData.size()>0);
}
public int size(){
return elementData.size();
}
}