01: /*
02: * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.
03: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
04: *
05: * This code is free software; you can redistribute it and/or modify it
06: * under the terms of the GNU General Public License version 2 only, as
07: * published by the Free Software Foundation. Sun designates this
08: * particular file as subject to the "Classpath" exception as provided
09: * by Sun in the LICENSE file that accompanied this code.
10: *
11: * This code is distributed in the hope that it will be useful, but WITHOUT
12: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14: * version 2 for more details (a copy is included in the LICENSE file that
15: * accompanied this code).
16: *
17: * You should have received a copy of the GNU General Public License version
18: * 2 along with this work; if not, write to the Free Software Foundation,
19: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20: *
21: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22: * CA 95054 USA or visit www.sun.com if you need additional information or
23: * have any questions.
24: */
25:
26: package com.sun.tools.internal.xjc.reader.gbind;
27:
28: import java.util.Set;
29:
30: /**
31: * This builds content models.
32: *
33: * @author Kohsuke Kawaguchi
34: */
35: public abstract class Expression {
36:
37: /**
38: * Computes <tt>LAST(exp)</tt>
39: */
40: abstract ElementSet lastSet();
41:
42: /**
43: * True of <tt>\epsilon \in L(exp)</tt>
44: */
45: abstract boolean isNullable();
46:
47: /**
48: * Builds up a DAG among {@link Element}s in this expression.
49: */
50: abstract void buildDAG(ElementSet incoming);
51:
52: /**
53: * {@link Expression} that represents epsilon, the length-0 string.
54: */
55: public static final Expression EPSILON = new Expression() {
56: ElementSet lastSet() {
57: return ElementSet.EMPTY_SET;
58: }
59:
60: boolean isNullable() {
61: return true;
62: }
63:
64: void buildDAG(ElementSet incoming) {
65: // noop
66: }
67:
68: void assignElementNumber(Set<Element> allElements) {
69: // noop
70: }
71:
72: public String toString() {
73: return "-";
74: }
75: };
76: }
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