/* This file is part of the db4o object database http://www.db4o.com
Copyright (C) 2004 - 2011 Versant Corporation http://www.versant.com
db4o is free software; you can redistribute it and/or modify it under
the terms of version 3 of the GNU General Public License as published
by the Free Software Foundation.
db4o is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License along
with this program. If not, see http://www.gnu.org/licenses/. */
package com.db4o.foundation;
/**
* @exclude
*/
public class Stack4 {
private List4 _tail;
public void push(Object obj) {
_tail = new List4(_tail, obj);
}
public Object peek() {
if(_tail == null){
return null;
}
return _tail._element;
}
public Object pop() {
if(_tail == null){
throw new IllegalStateException();
}
Object res = _tail._element;
_tail = _tail._next;
return res;
}
public boolean isEmpty() {
return _tail==null;
}
}