Source Code Cross Referenced for Expression.java in  » RSS-RDF » Jena-2.5.5 » com » hp » hpl » jena » graph » query » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » RSS RDF » Jena 2.5.5 » com.hp.hpl.jena.graph.query 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:          (c) Copyright 2003, 2004, 2005, 2006, 2007, 2008 Hewlett-Packard Development Company, LP, all rights reserved.
003:          [See end of file]
004:          $Id: Expression.java,v 1.29 2008/01/02 12:07:57 andy_seaborne Exp $
005:         */
006:
007:        package com.hp.hpl.jena.graph.query;
008:
009:        import java.util.*;
010:
011:        import com.hp.hpl.jena.util.CollectionFactory;
012:
013:        /**
014:         Expression - the interface for expressions that is expected by Query for 
015:         constraints. An Expression can be evaluated (given a name->value mapping);
016:         it can be prepared into a Valuator (given a name->index mapping); and it can
017:         be analysed into its components.
018:         <p>
019:         An Expression can be a variable, an application, or a literal value. If an access
020:         method (eg getName) is applied to an Expression for which it is not appropriate
021:         (eg an application), <em>the result is unspecified</em>; an implementation is
022:         free to throw an exception, deliver a null result, deliver a misleading value,
023:         whatever is convenient.
024:         <p>
025:         The nested class <code>Util</code> provides some expression utility
026:         methods, including a generic version of <code>prepare</code>. The nested 
027:         abstract class <code>Base</code> and its sub-classes <code>Literal</code>, 
028:         <code>Variable</code>, and <code>Application</code> provide a framework 
029:         for developers to implement Expressions over.
030:
031:         @author kers
032:         */
033:        public interface Expression {
034:            /**
035:                Answer a Valuator which, when run with a set of index-to-value bindings, 
036:                evaluates this expression in the light of the given variable-to-index bindings
037:                [ie as though the variables were bound to the corresponding values]
038:             */
039:            public Valuator prepare(VariableIndexes vi);
040:
041:            /**
042:            	Answer true iff this Expression represents a variable.
043:             */
044:            public boolean isVariable();
045:
046:            /**
047:                If this Expression is a variable, answer a [non-null] String which is its name.
048:                Otherwise the behaviour is unspecified.
049:             */
050:            public String getName();
051:
052:            /**
053:                Answer true iff this Expression represents a literal [Java object] value.
054:             */
055:            public boolean isConstant();
056:
057:            /**
058:                If this Expression is a literal, answer the value of that literal. Otherwise the
059:                behaviour is unspecified.
060:             */
061:            public Object getValue();
062:
063:            /**
064:                Answer true iff this Expression represents the application of some function
065:                [or operator] to some arguments [or operands].
066:             */
067:            public boolean isApply();
068:
069:            /**
070:                 If this Expression is an application, return the string identifying the function,
071:                 which should be a URI. Otherwise the behaviour is unspecified.
072:             */
073:            public String getFun();
074:
075:            /**
076:            	If this Expression is an application, answer the number of arguments that
077:                it has. Otherwise the behaviour is unspecified.    
078:             */
079:            public int argCount();
080:
081:            /**
082:                If this Expression is an application, and 0 &lt;= i &lt; argCount(), answer the
083:                <code>i</code>th argument. Otherwise the behaviour is unspecified. 
084:             */
085:            public Expression getArg(int i);
086:
087:            /**
088:            	An Expression which always evaluates to <code>true</code>.
089:             */
090:            public static Expression TRUE = new BoolConstant(true);
091:
092:            /**
093:                An Expression which always evaluates to <code>false</code>.
094:             */
095:            public static Expression FALSE = new BoolConstant(false);
096:
097:            /**
098:                An abstract base class for Expressions; over-ride as appropriate. The
099:                sub-classes may be more useful. 
100:             */
101:            public static abstract class Base implements  Expression {
102:                public boolean isVariable() {
103:                    return false;
104:                }
105:
106:                public boolean isApply() {
107:                    return false;
108:                }
109:
110:                public boolean isConstant() {
111:                    return false;
112:                }
113:
114:                public String getName() {
115:                    return null;
116:                }
117:
118:                public Object getValue() {
119:                    return null;
120:                }
121:
122:                public int argCount() {
123:                    return 0;
124:                }
125:
126:                public String getFun() {
127:                    return null;
128:                }
129:
130:                public Expression getArg(int i) {
131:                    return null;
132:                }
133:
134:                public boolean equals(Object other) {
135:                    return other instanceof  Expression
136:                            && Expression.Util.equals(this , (Expression) other);
137:                }
138:            }
139:
140:            /**
141:                An abstract base class for literal nodes; subclasses implement getValue().
142:             */
143:            public static abstract class Constant extends Base {
144:                public boolean isConstant() {
145:                    return true;
146:                }
147:
148:                public abstract Object getValue();
149:            }
150:
151:            /**
152:             	A concrete class for representing fixed constants; each instance
153:             	can hold a separate value and its valuator returns that value.
154:             */
155:            public static class Fixed extends Constant {
156:                protected Object value;
157:
158:                public Fixed(Object value) {
159:                    this .value = value;
160:                }
161:
162:                public Object getValue() {
163:                    return value;
164:                }
165:
166:                public Valuator prepare(VariableIndexes vi) {
167:                    return new FixedValuator(value);
168:                }
169:
170:                public String toString() {
171:                    return value.toString();
172:                }
173:            }
174:
175:            /**
176:                An abstract base class for variable nodes; subclasses implement getName().
177:             */
178:            public static abstract class Variable extends Base {
179:                public boolean isVariable() {
180:                    return true;
181:                }
182:
183:                public abstract String getName();
184:            }
185:
186:            /**
187:                An abstract base class for apply nodes; subclasses implement getFun(),
188:                argCount(), and getArg().
189:             */
190:            public static abstract class Application extends Base {
191:                public boolean isApply() {
192:                    return true;
193:                }
194:
195:                public abstract int argCount();
196:
197:                public abstract String getFun();
198:
199:                public abstract Expression getArg(int i);
200:            }
201:
202:            /**
203:                Utility methods for Expressions, captured in a class because they can't be
204:                written directly in the interface.
205:             */
206:            public static class Util {
207:                /**
208:                    Answer a set containing exactly the names of variables within 
209:                    <code>e</code>.
210:                 */
211:                public static Set variablesOf(Expression e) {
212:                    return addVariablesOf(CollectionFactory.createHashedSet(),
213:                            e);
214:                }
215:
216:                /**
217:                    Add all the variables of <code>e</code> to <code>s</code>, and answer
218:                    <code>s</code>.
219:                 */
220:                public static Set addVariablesOf(Set s, Expression e) {
221:                    if (e.isVariable())
222:                        s.add(e.getName());
223:                    else if (e.isApply())
224:                        for (int i = 0; i < e.argCount(); i += 1)
225:                            addVariablesOf(s, e.getArg(i));
226:                    return s;
227:                }
228:
229:                public static boolean containsAllVariablesOf(Set variables,
230:                        Expression e) {
231:                    if (e.isConstant())
232:                        return true;
233:                    if (e.isVariable())
234:                        return variables.contains(e.getName());
235:                    if (e.isApply()) {
236:                        for (int i = 0; i < e.argCount(); i += 1)
237:                            if (containsAllVariablesOf(variables, e.getArg(i)) == false)
238:                                return false;
239:                        return true;
240:                    }
241:                    return false;
242:                }
243:
244:                public static boolean equals(Expression L, Expression R) {
245:                    return L.isConstant() ? R.isConstant()
246:                            && L.getValue().equals(R.getValue()) : L
247:                            .isVariable() ? R.isVariable()
248:                            && R.getName().equals(R.getName())
249:                            : L.isApply() ? R.isApply() && sameApply(L, R)
250:                                    : false;
251:                }
252:
253:                public static boolean sameApply(Expression L, Expression R) {
254:                    return L.argCount() == R.argCount()
255:                            && L.getFun().equals(R.getFun()) && sameArgs(L, R);
256:                }
257:
258:                public static boolean sameArgs(Expression L, Expression R) {
259:                    for (int i = 0; i < L.argCount(); i += 1)
260:                        if (!equals(L.getArg(i), R.getArg(i)))
261:                            return false;
262:                    return true;
263:                }
264:            }
265:
266:            /**
267:            	Valof provides an implementation of VariableValues which composes the
268:                "compile-time" VariableIndexes map with the "run-time" IndexValues map
269:                to produce a VariableValues map. A Valof has mutable state; the setDomain
270:                operation changes the IndexValues mapping of the Valof.
271:            
272:            	@author kers
273:             */
274:            static class Valof implements  VariableValues {
275:                private VariableIndexes map;
276:                private IndexValues dom;
277:
278:                public Valof(VariableIndexes map) {
279:                    this .map = map;
280:                }
281:
282:                public final Object get(String name) {
283:                    return dom.get(map.indexOf(name));
284:                }
285:
286:                public final Valof setDomain(IndexValues d) {
287:                    dom = d;
288:                    return this ;
289:                }
290:            }
291:
292:            /**
293:            	Base class used to implement <code>TRUE</code> and <code>FALSE</code>.
294:             */
295:            public static class BoolConstant extends Base implements 
296:                    Expression, Valuator {
297:                private boolean value;
298:
299:                public BoolConstant(boolean value) {
300:                    this .value = value;
301:                }
302:
303:                public boolean isConstant() {
304:                    return true;
305:                }
306:
307:                // TODO when moving to Jave 1.4 can use Boolean.valueOf( value )
308:                public Object getValue() {
309:                    return value ? Boolean.TRUE : Boolean.FALSE;
310:                }
311:
312:                public Valuator prepare(VariableIndexes vi) {
313:                    return this ;
314:                }
315:
316:                public boolean evalBool(VariableValues vv) {
317:                    return value;
318:                }
319:
320:                public boolean evalBool(IndexValues vv) {
321:                    return value;
322:                }
323:
324:                public Object evalObject(IndexValues iv) {
325:                    return getValue();
326:                }
327:            }
328:        }
329:
330:        /*
331:         (c) Copyright 2003, 2004, 2005, 2006, 2007, 2008 Hewlett-Packard Development Company, LP
332:         All rights reserved.
333:
334:         Redistribution and use in source and binary forms, with or without
335:         modification, are permitted provided that the following conditions
336:         are met:
337:
338:         1. Redistributions of source code must retain the above copyright
339:         notice, this list of conditions and the following disclaimer.
340:
341:         2. Redistributions in binary form must reproduce the above copyright
342:         notice, this list of conditions and the following disclaimer in the
343:         documentation and/or other materials provided with the distribution.
344:
345:         3. The name of the author may not be used to endorse or promote products
346:         derived from this software without specific prior written permission.
347:
348:         THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
349:         IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
350:         OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
351:         IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
352:         INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
353:         NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
354:         DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
355:         THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
356:         (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
357:         THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
358:         */
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