package com.zzk.coding2017.zuoye_1;
public class Stack {
private ArrayList elementData = new ArrayList();
public void push(Object o){
elementData.add(o);
}
public Object pop(){
if(elementData.size()==0){
return null;
}
else{
Object result = elementData.get(elementData.size()-1);
elementData.remove(elementData.size()-1);
return result;
}
}
public Object peek(){
if(elementData.size()==0){
return null;
}
else{
return elementData.get(elementData.size()-1);
}
}
public boolean isEmpty(){
if(elementData.size()==0)
return true;
else
return false;
}
public int size(){
return elementData.size();
}
}