Source Code Cross Referenced for Expression.java in  » Library » Apache-commons-jxpath-1.2-src » org » apache » commons » jxpath » ri » compiler » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Library » Apache commons jxpath 1.2 src » org.apache.commons.jxpath.ri.compiler 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Copyright 1999-2004 The Apache Software Foundation
003:         *
004:         * Licensed under the Apache License, Version 2.0 (the "License");
005:         * you may not use this file except in compliance with the License.
006:         * You may obtain a copy of the License at
007:         *
008:         *     http://www.apache.org/licenses/LICENSE-2.0
009:         *
010:         * Unless required by applicable law or agreed to in writing, software
011:         * distributed under the License is distributed on an "AS IS" BASIS,
012:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013:         * See the License for the specific language governing permissions and
014:         * limitations under the License.
015:         */
016:        package org.apache.commons.jxpath.ri.compiler;
017:
018:        import org.apache.commons.jxpath.Pointer;
019:        import org.apache.commons.jxpath.ri.EvalContext;
020:        import org.apache.commons.jxpath.ri.model.NodePointer;
021:        import org.apache.commons.jxpath.ri.QName;
022:        import org.apache.commons.jxpath.util.ValueUtils;
023:
024:        import java.util.Collections;
025:        import java.util.Iterator;
026:        import java.util.Locale;
027:
028:        /**
029:         * Common superclass for several types of nodes in the parse tree. Provides
030:         * APIs for optimization of evaluation of expressions.  Specifically, an
031:         * expression only needs to executed once during the evaluation of an xpath
032:         * if that expression is context-independent.  Expression.isContextDependent()
033:         * provides that hint.
034:         *
035:         * @author Dmitri Plotnikov
036:         * @version $Revision: 1.10 $ $Date: 2004/02/29 14:17:38 $
037:         */
038:        public abstract class Expression {
039:
040:            protected static final Double ZERO = new Double(0);
041:            protected static final Double ONE = new Double(1);
042:            protected static final Double NOT_A_NUMBER = new Double(Double.NaN);
043:
044:            private boolean contextDependencyKnown = false;
045:            private boolean contextDependent;
046:
047:            /**
048:             * Returns true if this expression should be re-evaluated
049:             * each time the current position in the context changes.
050:             */
051:            public boolean isContextDependent() {
052:                if (!contextDependencyKnown) {
053:                    contextDependent = computeContextDependent();
054:                    contextDependencyKnown = true;
055:                }
056:                return contextDependent;
057:            }
058:
059:            /**
060:             * Implemented by subclasses and result is cached by isContextDependent()
061:             */
062:            public abstract boolean computeContextDependent();
063:
064:            /**
065:             * Evaluates the expression. If the result is a node set, returns
066:             * the first element of the node set.
067:             */
068:            public abstract Object computeValue(EvalContext context);
069:
070:            public abstract Object compute(EvalContext context);
071:
072:            public Iterator iterate(EvalContext context) {
073:                Object result = compute(context);
074:                if (result instanceof  EvalContext) {
075:                    return new ValueIterator((EvalContext) result);
076:                }
077:                return ValueUtils.iterate(result);
078:            }
079:
080:            public Iterator iteratePointers(EvalContext context) {
081:                Object result = compute(context);
082:                if (result == null) {
083:                    return Collections.EMPTY_LIST.iterator();
084:                }
085:                if (result instanceof  EvalContext) {
086:                    return (EvalContext) result;
087:                }
088:                return new PointerIterator(ValueUtils.iterate(result),
089:                        new QName(null, "value"), context.getRootContext()
090:                                .getCurrentNodePointer().getLocale());
091:            }
092:
093:            public static class PointerIterator implements  Iterator {
094:                private Iterator iterator;
095:                private QName qname;
096:                private Locale locale;
097:
098:                /**
099:                 * @deprecated Use the method that takes a NamespaceManager
100:                 */
101:                public PointerIterator(Iterator it, QName qname, Locale locale) {
102:                    this .iterator = it;
103:                    this .qname = qname;
104:                    this .locale = locale;
105:                }
106:
107:                public boolean hasNext() {
108:                    return iterator.hasNext();
109:                }
110:
111:                public Object next() {
112:                    Object o = iterator.next();
113:                    return NodePointer.newNodePointer(qname, o, locale);
114:                }
115:
116:                public void remove() {
117:                    throw new UnsupportedOperationException();
118:                }
119:            }
120:
121:            public static class ValueIterator implements  Iterator {
122:                private Iterator iterator;
123:
124:                public ValueIterator(Iterator it) {
125:                    this .iterator = it;
126:                }
127:
128:                public boolean hasNext() {
129:                    return iterator.hasNext();
130:                }
131:
132:                public Object next() {
133:                    Object o = iterator.next();
134:                    if (o instanceof  Pointer) {
135:                        return ((Pointer) o).getValue();
136:                    }
137:                    return o;
138:                }
139:
140:                public void remove() {
141:                    throw new UnsupportedOperationException();
142:                }
143:            }
144:        }
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