1 /* 2 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * 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 {@code LAST(exp)} 39 */ 40 abstract ElementSet lastSet(); 41 42 /** 43 * True of {@code \epsilon \in L(exp)} 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 public String toString() { 69 return "-"; 70 } 71 }; 72 }