package code01;
public class Stack {
private ArrayList elementData = new ArrayList();
public void push(Object o){
elementData.add(o);
}
public Object pop(){
Object result = null;
if(elementData.size()!=0) {
result = elementData.remove(elementData.size() - 1);
}
return result;
}
public Object peek(){
Object result = null;
if(elementData.size()!=0) {
result = elementData.get(elementData.size() - 1);
}
return result;
}
public boolean isEmpty(){
return elementData.size() == 0;
}
public int size(){
return elementData.size();
}
}