Source Code Cross Referenced for Expression.java in  » XML » saxonb » net » sf » saxon » expr » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.expr 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.expr;
002:
003:        import net.sf.saxon.om.Item;
004:        import net.sf.saxon.om.NamePool;
005:        import net.sf.saxon.om.SequenceIterator;
006:        import net.sf.saxon.trans.XPathException;
007:        import net.sf.saxon.type.ItemType;
008:        import net.sf.saxon.type.SchemaType;
009:        import net.sf.saxon.type.TypeHierarchy;
010:
011:        import java.io.PrintStream;
012:        import java.io.Serializable;
013:        import java.util.Iterator;
014:
015:        /**
016:         * Interface supported by an XPath expression. This includes both compile-time
017:         * and run-time methods.
018:         */
019:
020:        public interface Expression extends Serializable {
021:
022:            public static final int EVALUATE_METHOD = 1;
023:            public static final int ITERATE_METHOD = 2;
024:            public static final int PROCESS_METHOD = 4;
025:
026:            /**
027:             * An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
028:             * This method indicates which of these methods is provided directly. The other methods will always be available
029:             * indirectly, using an implementation that relies on one of the other methods.
030:             */
031:
032:            public int getImplementationMethod();
033:
034:            /**
035:             * Simplify an expression. This performs any static optimization (by rewriting the expression
036:             * as a different expression). The default implementation does nothing.
037:             *
038:             * @exception net.sf.saxon.trans.StaticError if an error is discovered during expression
039:             *     rewriting
040:             * @return the simplified expression
041:             */
042:
043:            Expression simplify(StaticContext env) throws XPathException;
044:
045:            /**
046:             * Perform type checking of an expression and its subexpressions.
047:             *
048:             * <p>This checks statically that the operands of the expression have
049:             * the correct type; if necessary it generates code to do run-time type checking or type
050:             * conversion. A static type error is reported only if execution cannot possibly succeed, that
051:             * is, if a run-time type error is inevitable. The call may return a modified form of the expression.</p>
052:             *
053:             * <p>This method is called after all references to functions and variables have been resolved
054:             * to the declaration of the function or variable. However, the types of such functions and
055:             * variables may not be accurately known if they have not been explicitly declared.</p>
056:             *
057:             * @param env the static context of the expression
058:             * @param contextItemType the static type of "." at the point where this expression is invoked.
059:             * The parameter is set to null if it is known statically that the context item will be undefined.
060:             * If the type of the context item is not known statically, the argument is set to
061:             * {@link net.sf.saxon.type.Type#ITEM_TYPE}
062:             * @exception net.sf.saxon.trans.StaticError if an error is discovered during this phase
063:             *     (typically a type error)
064:             * @return the original expression, rewritten to perform necessary
065:             *     run-time type checks, and to perform other type-related
066:             *     optimizations
067:             */
068:
069:            Expression typeCheck(StaticContext env, ItemType contextItemType)
070:                    throws XPathException;
071:
072:            /**
073:             * Perform optimisation of an expression and its subexpressions.
074:             *
075:             * <p>This method is called after all references to functions and variables have been resolved
076:             * to the declaration of the function or variable, and after all type checking has been done.</p>
077:             * @param opt the optimizer in use. This provides access to supporting functions; it also allows
078:             * different optimization strategies to be used in different circumstances.
079:             * @param env the static context of the expression
080:             * @param contextItemType the static type of "." at the point where this expression is invoked.
081:             * The parameter is set to null if it is known statically that the context item will be undefined.
082:             * If the type of the context item is not known statically, the argument is set to
083:             * {@link net.sf.saxon.type.Type#ITEM_TYPE}
084:             * @exception net.sf.saxon.trans.StaticError if an error is discovered during this phase
085:             *     (typically a type error)
086:             * @return the original expression, rewritten if appropriate to optimize execution
087:             */
088:
089:            Expression optimize(Optimizer opt, StaticContext env,
090:                    ItemType contextItemType) throws XPathException;
091:
092:            /**
093:             * Offer promotion for this subexpression. The offer will be accepted if the subexpression
094:             * is not dependent on the factors (e.g. the context item) identified in the PromotionOffer.
095:             * By default the offer is not accepted - this is appropriate in the case of simple expressions
096:             * such as constant values and variable references where promotion would give no performance
097:             * advantage. This method is always called at compile time.
098:             *
099:             * @param offer details of the offer, for example the offer to move
100:             *     expressions that don't depend on the context to an outer level in
101:             *     the containing expression
102:             * @exception net.sf.saxon.trans.XPathException if any error is detected
103:             * @return if the offer is not accepted, return this expression unchanged.
104:             *      Otherwise return the result of rewriting the expression to promote
105:             *      this subexpression
106:             */
107:
108:            Expression promote(PromotionOffer offer) throws XPathException;
109:
110:            /**
111:             * Get the static properties of this expression (other than its type). The result is
112:             * bit-signficant. These properties are used for optimizations. In general, if
113:             * property bit is set, it is true, but if it is unset, the value is unknown.
114:             *
115:             * @return a set of flags indicating static properties of this expression
116:             */
117:
118:            int getSpecialProperties();
119:
120:            /**
121:             * <p>Determine the static cardinality of the expression. This establishes how many items
122:             * there will be in the result of the expression, at compile time (i.e., without
123:             * actually evaluating the result.</p>
124:             *
125:             * <p>This method should always return a result, though it may be the best approximation
126:             * that is available at the time.</p>
127:             *
128:             * @return one of the values {@link StaticProperty#ALLOWS_ONE},
129:             *     {@link StaticProperty#ALLOWS_ZERO_OR_MORE}, {@link StaticProperty#ALLOWS_ZERO_OR_ONE},
130:             *     {@link StaticProperty#ALLOWS_ONE_OR_MORE}, {@link StaticProperty#EMPTY}. This default
131:             *     implementation returns ZERO_OR_MORE (which effectively gives no
132:             *     information).
133:             */
134:
135:            int getCardinality();
136:
137:            /**
138:             * Determine the data type of the expression, if possible. All expression return
139:             * sequences, in general; this method determines the type of the items within the
140:             * sequence, assuming that (a) this is known in advance, and (b) it is the same for
141:             * all items in the sequence.
142:             *
143:             * <p>This method should always return a result, though it may be the best approximation
144:             * that is available at the time.</p>
145:             *
146:             * @return a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
147:             *     Type.NODE, or Type.ITEM (meaning not known at compile time)
148:             * @param th
149:             */
150:
151:            ItemType getItemType(TypeHierarchy th);
152:
153:            /**
154:             * Determine which aspects of the context the expression depends on. The result is
155:             * a bitwise-or'ed value composed from constants such as {@link StaticProperty#DEPENDS_ON_CONTEXT_ITEM} and
156:             * {@link StaticProperty#DEPENDS_ON_CURRENT_ITEM}. The default implementation combines the intrinsic
157:             * dependencies of this expression with the dependencies of the subexpressions,
158:             * computed recursively. This is overridden for expressions such as FilterExpression
159:             * where a subexpression's dependencies are not necessarily inherited by the parent
160:             * expression.
161:             *
162:             * @return a set of bit-significant flags identifying the dependencies of
163:             *     the expression
164:             */
165:
166:            int getDependencies();
167:
168:            /**
169:             * Get the immediate sub-expressions of this expression. Default implementation
170:             * returns a zero-length array, appropriate for an expression that has no
171:             * sub-expressions.
172:             * @return an iterator containing the sub-expressions of this expression
173:             */
174:
175:            Iterator iterateSubExpressions();
176:
177:            /**
178:             * Get the container that immediately contains this expression. This method
179:             * returns null for an outermost expression; it also return null in the case
180:             * of literal values. For an XPath expression occurring within an XSLT stylesheet,
181:             * this method returns the XSLT instruction containing the XPath expression.
182:             * @return the expression that contains this expression, if known; return null
183:             * if there is no containing expression or if the containing expression is unknown.
184:             */
185:
186:            Container getParentExpression();
187:
188:            /**
189:             * Test if this expression is the same as another expression.
190:             * (Note, returns false to indicate "don't know": our tests are rather limited)
191:             *
192:             * @param other the expression to be compared with this one
193:             * @return true if this expression is known to be equivalent to the other
194:             *     expression (that is, to deliver the same result in all
195:             *     circumstances, assuming the context is the same)
196:             */
197:
198:            //boolean equals(Object other);
199:
200:            /**
201:             * Evaluate an expression as a single item. This always returns either a single Item or
202:             * null (denoting the empty sequence). No conversion is done. This method should not be
203:             * used unless the static type of the expression is a subtype of "item" or "item?": that is,
204:             * it should not be called if the expression may return a sequence. There is no guarantee that
205:             * this condition will be detected.
206:             *
207:             * @param context The context in which the expression is to be evaluated
208:             * @exception XPathException if any dynamic error occurs evaluating the
209:             *     expression
210:             * @return the node or atomic value that results from evaluating the
211:             *     expression; or null to indicate that the result is an empty
212:             *     sequence
213:             */
214:
215:            Item evaluateItem(XPathContext context) throws XPathException;
216:
217:            /**
218:             * Return an Iterator to iterate over the values of a sequence. The value of every
219:             * expression can be regarded as a sequence, so this method is supported for all
220:             * expressions. This default implementation handles iteration for expressions that
221:             * return singleton values: for non-singleton expressions, the subclass must
222:             * provide its own implementation.
223:             *
224:             * @exception net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the
225:             *     expression
226:             * @param context supplies the context for evaluation
227:             * @return a SequenceIterator that can be used to iterate over the result
228:             *     of the expression
229:             */
230:
231:            SequenceIterator iterate(XPathContext context)
232:                    throws XPathException;
233:
234:            /**
235:             * Get the effective boolean value of the expression. This returns false if the value
236:             * is the empty sequence, a zero-length string, a number equal to zero, or the boolean
237:             * false. Otherwise it returns true.
238:             *
239:             * @param context The context in which the expression is to be evaluated
240:             * @exception net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the
241:             *     expression
242:             * @return the effective boolean value
243:             */
244:
245:            boolean effectiveBooleanValue(XPathContext context)
246:                    throws XPathException;
247:
248:            /**
249:             * Evaluate an expression as a String. This function must only be called in contexts
250:             * where it is known that the expression will return a single string (or where an empty sequence
251:             * is to be treated as a zero-length string). Implementations should not attempt to convert
252:             * the result to a string, other than converting () to "". This method is used mainly to
253:             * evaluate expressions produced by compiling an attribute value template.
254:             *
255:             * @exception XPathException if any dynamic error occurs evaluating the
256:             *     expression
257:             * @exception ClassCastException if the result type of the
258:             *     expression is not xs:string?
259:             * @param context The context in which the expression is to be evaluated
260:             * @return the value of the expression, evaluated in the current context.
261:             *     The expression must return a string or (); if the value of the
262:             *     expression is (), this method returns "".
263:             */
264:
265:            public String evaluateAsString(XPathContext context)
266:                    throws XPathException;
267:
268:            /**
269:             * Process the instruction, without returning any tail calls
270:             * @param context The dynamic context, giving access to the current node,
271:             * the current variables, etc.
272:             */
273:
274:            public void process(XPathContext context) throws XPathException;
275:
276:            /**
277:             * Diagnostic print of expression structure. The expression is written to the System.err
278:             * output stream
279:             *
280:             * @param level indentation level for this expression
281:             * @param pool NamePool used to expand any names appearing in the expression
282:             * @param out Output destination
283:             */
284:
285:            public void display(int level, NamePool pool, PrintStream out);
286:
287:            /**
288:             * Check statically that the results of the expression are capable of constructing the content
289:             * of a given schema type.
290:             * @param parentType The schema type
291:             * @param env the static context
292:             * @param whole true if this expression is expected to make the whole content of the type, false
293:             * if it is expected to make up only a part
294:             * @throws XPathException if the expression doesn't match the required content type
295:             */
296:
297:            public void checkPermittedContents(SchemaType parentType,
298:                    StaticContext env, boolean whole) throws XPathException;
299:        }
300:        //
301:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
302:        // you may not use this file except in compliance with the License. You may obtain a copy of the
303:        // License at http://www.mozilla.org/MPL/
304:        //
305:        // Software distributed under the License is distributed on an "AS IS" basis,
306:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
307:        // See the License for the specific language governing rights and limitations under the License.
308:        //
309:        // The Original Code is: all this file.
310:        //
311:        // The Initial Developer of the Original Code is Michael H. Kay.
312:        //
313:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
314:        //
315:        // Contributor(s): none.
316:        //
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