001: /*
002: * Copyright (c) 2003 The Visigoth Software Society. All rights
003: * reserved.
004: *
005: * Redistribution and use in source and binary forms, with or without
006: * modification, are permitted provided that the following conditions
007: * are met:
008: *
009: * 1. Redistributions of source code must retain the above copyright
010: * notice, this list of conditions and the following disclaimer.
011: *
012: * 2. Redistributions in binary form must reproduce the above copyright
013: * notice, this list of conditions and the following disclaimer in
014: * the documentation and/or other materials provided with the
015: * distribution.
016: *
017: * 3. The end-user documentation included with the redistribution, if
018: * any, must include the following acknowledgement:
019: * "This product includes software developed by the
020: * Visigoth Software Society (http://www.visigoths.org/)."
021: * Alternately, this acknowledgement may appear in the software itself,
022: * if and wherever such third-party acknowledgements normally appear.
023: *
024: * 4. Neither the name "FreeMarker", "Visigoth", nor any of the names of the
025: * project contributors may be used to endorse or promote products derived
026: * from this software without prior written permission. For written
027: * permission, please contact visigoths@visigoths.org.
028: *
029: * 5. Products derived from this software may not be called "FreeMarker" or "Visigoth"
030: * nor may "FreeMarker" or "Visigoth" appear in their names
031: * without prior written permission of the Visigoth Software Society.
032: *
033: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
034: * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
035: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
036: * DISCLAIMED. IN NO EVENT SHALL THE VISIGOTH SOFTWARE SOCIETY OR
037: * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
038: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
039: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
040: * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
041: * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
042: * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
043: * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
044: * SUCH DAMAGE.
045: * ====================================================================
046: *
047: * This software consists of voluntary contributions made by many
048: * individuals on behalf of the Visigoth Software Society. For more
049: * information on the Visigoth Software Society, please see
050: * http://www.visigoths.org/
051: */
052:
053: package freemarker.template;
054:
055: import java.util.List;
056: import java.util.ArrayList;
057:
058: /**
059: * Singleton object representing nothing, used by ?if_exists built-in.
060: * It is meant to be interpreted in the most sensible way possible in various contexts.
061: * This can be returned to avoid exceptions.
062: *
063: * @author <a href="mailto:jon@revusky.com">Jonathan Revusky</a>
064: */
065:
066: final class GeneralPurposeNothing implements TemplateBooleanModel,
067: TemplateScalarModel, TemplateSequenceModel,
068: TemplateHashModelEx, TemplateMethodModelEx {
069:
070: private static final TemplateModel instance = new GeneralPurposeNothing();
071:
072: private static final TemplateCollectionModel EMPTY_COLLECTION = new SimpleCollection(
073: new ArrayList(0));
074:
075: private GeneralPurposeNothing() {
076: }
077:
078: static TemplateModel getInstance() {
079: return instance;
080: }
081:
082: public String getAsString() {
083: return "";
084: }
085:
086: public boolean getAsBoolean() {
087: return false;
088: }
089:
090: public boolean isEmpty() {
091: return true;
092: }
093:
094: public int size() {
095: return 0;
096: }
097:
098: public TemplateModel get(int i) throws TemplateModelException {
099: throw new TemplateModelException("Empty list");
100: }
101:
102: public TemplateModel get(String key) {
103: return null;
104: }
105:
106: public Object exec(List args) {
107: return null;
108: }
109:
110: public TemplateCollectionModel keys() {
111: return EMPTY_COLLECTION;
112: }
113:
114: public TemplateCollectionModel values() {
115: return EMPTY_COLLECTION;
116: }
117: }
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