01: /* Copyright (C) 2004 - 2007 db4objects Inc. http://www.db4o.com
02:
03: This file is part of the db4o open source object database.
04:
05: db4o is free software; you can redistribute it and/or modify it under
06: the terms of version 2 of the GNU General Public License as published
07: by the Free Software Foundation and as clarified by db4objects' GPL
08: interpretation policy, available at
09: http://www.db4o.com/about/company/legalpolicies/gplinterpretation/
10: Alternatively you can write to db4objects, Inc., 1900 S Norfolk Street,
11: Suite 350, San Mateo, CA 94403, USA.
12:
13: db4o is distributed in the hope that it will be useful, but WITHOUT ANY
14: WARRANTY; without even the implied warranty of MERCHANTABILITY or
15: FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16: for more details.
17:
18: You should have received a copy of the GNU General Public License along
19: with this program; if not, write to the Free Software Foundation, Inc.,
20: 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
21: package com.db4o.foundation;
22:
23: /**
24: * @exclude
25: */
26: public class Stack4 {
27:
28: private List4 _tail;
29:
30: public void push(Object obj) {
31: _tail = new List4(_tail, obj);
32: }
33:
34: public Object peek() {
35: if (_tail == null) {
36: return null;
37: }
38: return _tail._element;
39: }
40:
41: public Object pop() {
42: if (_tail == null) {
43: throw new IllegalStateException();
44: }
45: Object res = _tail._element;
46: _tail = _tail._next;
47: return res;
48: }
49:
50: public boolean isEmpty() {
51: return _tail == null;
52: }
53:
54: }
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