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Java example source code file (FilterExpr.java)

This example Java source code file (FilterExpr.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

castexpr, constantpoolgen, current_node_list_filter_sig, expression, filterexpr, invokespecial, localvariablegen, methodgenerator, node_iterator_sig, node_sig\+translet_sig, predicate, string, typecheckerror, util, vector

The FilterExpr.java Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
/*
 * Copyright 2001-2005 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: FilterExpr.java,v 1.2.4.1 2005/09/12 10:22:50 pvedula Exp $
 */

package com.sun.org.apache.xalan.internal.xsltc.compiler;

import java.util.Vector;

import com.sun.org.apache.bcel.internal.generic.ALOAD;
import com.sun.org.apache.bcel.internal.generic.ASTORE;
import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;
import com.sun.org.apache.bcel.internal.generic.ILOAD;
import com.sun.org.apache.bcel.internal.generic.INVOKEINTERFACE;
import com.sun.org.apache.bcel.internal.generic.INVOKESPECIAL;
import com.sun.org.apache.bcel.internal.generic.INVOKESTATIC;
import com.sun.org.apache.bcel.internal.generic.InstructionList;
import com.sun.org.apache.bcel.internal.generic.ISTORE;
import com.sun.org.apache.bcel.internal.generic.LocalVariableGen;
import com.sun.org.apache.bcel.internal.generic.NEW;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ClassGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.MethodGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.NodeSetType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ReferenceType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.Type;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.TypeCheckError;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.Util;

/**
 * @author Jacek Ambroziak
 * @author Santiago Pericas-Geertsen
 * @author Morten Jorgensen
 */
class FilterExpr extends Expression {

    /**
     * Primary expression of this filter. I.e., 'e' in '(e)[p1]...[pn]'.
     */
    private Expression   _primary;

    /**
     * Array of predicates in '(e)[p1]...[pn]'.
     */
    private final Vector _predicates;

    public FilterExpr(Expression primary, Vector predicates) {
        _primary = primary;
        _predicates = predicates;
        primary.setParent(this);
    }

    protected Expression getExpr() {
        if (_primary instanceof CastExpr)
            return ((CastExpr)_primary).getExpr();
        else
            return _primary;
    }

    public void setParser(Parser parser) {
        super.setParser(parser);
        _primary.setParser(parser);
        if (_predicates != null) {
            final int n = _predicates.size();
            for (int i = 0; i < n; i++) {
                final Expression exp = (Expression)_predicates.elementAt(i);
                exp.setParser(parser);
                exp.setParent(this);
            }
        }
    }

    public String toString() {
        return "filter-expr(" + _primary + ", " + _predicates + ")";
    }

    /**
     * Type check a FilterParentPath. If the filter is not a node-set add a
     * cast to node-set only if it is of reference type. This type coercion
     * is needed for expressions like $x where $x is a parameter reference.
     * All optimizations are turned off before type checking underlying
     * predicates.
     */
    public Type typeCheck(SymbolTable stable) throws TypeCheckError {
        Type ptype = _primary.typeCheck(stable);
        boolean canOptimize = _primary instanceof KeyCall;

        if (ptype instanceof NodeSetType == false) {
            if (ptype instanceof ReferenceType)  {
                _primary = new CastExpr(_primary, Type.NodeSet);
            }
            else {
                throw new TypeCheckError(this);
            }
        }

        // Type check predicates and turn all optimizations off if appropriate
        int n = _predicates.size();
        for (int i = 0; i < n; i++) {
            Predicate pred = (Predicate) _predicates.elementAt(i);

            if (!canOptimize) {
                pred.dontOptimize();
            }
            pred.typeCheck(stable);
        }
        return _type = Type.NodeSet;
    }

    /**
     * Translate a filter expression by pushing the appropriate iterator
     * onto the stack.
     */
    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
        translateFilterExpr(classGen, methodGen, _predicates == null ? -1 : _predicates.size() - 1);
    }

    private void translateFilterExpr(ClassGenerator classGen,
                                     MethodGenerator methodGen,
                                     int predicateIndex) {
        if (predicateIndex >= 0) {
            translatePredicates(classGen, methodGen, predicateIndex);
        }
        else {
            _primary.translate(classGen, methodGen);
        }
    }

    /**
     * Translate a sequence of predicates. Each predicate is translated
     * by constructing an instance of <code>CurrentNodeListIterator
     * which is initialized from another iterator (recursive call), a
     * filter and a closure (call to translate on the predicate) and "this".
     */
    public void translatePredicates(ClassGenerator classGen,
                                    MethodGenerator methodGen,
                                    int predicateIndex) {
        final ConstantPoolGen cpg = classGen.getConstantPool();
        final InstructionList il = methodGen.getInstructionList();

        // If not predicates left, translate primary expression
        if (predicateIndex < 0) {
            translateFilterExpr(classGen, methodGen, predicateIndex);
        }
        else {
            // Get the next predicate to be translated
            Predicate predicate = (Predicate) _predicates.get(predicateIndex--);

            // Translate the rest of the predicates from right to left
            translatePredicates(classGen, methodGen, predicateIndex);

            if (predicate.isNthPositionFilter()) {
                int nthIteratorIdx = cpg.addMethodref(NTH_ITERATOR_CLASS,
                                       "<init>",
                                       "("+NODE_ITERATOR_SIG+"I)V");

                // Backwards branches are prohibited if an uninitialized object
                // is on the stack by section 4.9.4 of the JVM Specification,
                // 2nd Ed.  We don't know whether this code might contain
                // backwards branches, so we mustn't create the new object unti

                // after we've created the suspect arguments to its constructor

                // Instead we calculate the values of the arguments to the
                // constructor first, store them in temporary variables, create
                // the object and reload the arguments from the temporaries to
                // avoid the problem.
                LocalVariableGen iteratorTemp
                        = methodGen.addLocalVariable("filter_expr_tmp1",
                                         Util.getJCRefType(NODE_ITERATOR_SIG),
                                         null, null);
                iteratorTemp.setStart(
                        il.append(new ASTORE(iteratorTemp.getIndex())));

                predicate.translate(classGen, methodGen);
                LocalVariableGen predicateValueTemp
                        = methodGen.addLocalVariable("filter_expr_tmp2",
                                         Util.getJCRefType("I"),
                                         null, null);
                predicateValueTemp.setStart(
                        il.append(new ISTORE(predicateValueTemp.getIndex())));

                il.append(new NEW(cpg.addClass(NTH_ITERATOR_CLASS)));
                il.append(DUP);
                iteratorTemp.setEnd(
                        il.append(new ALOAD(iteratorTemp.getIndex())));
                predicateValueTemp.setEnd(
                        il.append(new ILOAD(predicateValueTemp.getIndex())));
                il.append(new INVOKESPECIAL(nthIteratorIdx));
            } else {
                    // Translate predicates from right to left
                final int initCNLI = cpg.addMethodref(CURRENT_NODE_LIST_ITERATOR,
                                                      "<init>",
                                                      "("+NODE_ITERATOR_SIG+"Z"+
                                                      CURRENT_NODE_LIST_FILTER_SIG +
                                                      NODE_SIG+TRANSLET_SIG+")V");

                // Backwards branches are prohibited if an uninitialized object is
                // on the stack by section 4.9.4 of the JVM Specification, 2nd Ed.
                // We don't know whether this code might contain backwards branches,
                // so we mustn't create the new object until after we've created
                // the suspect arguments to its constructor.  Instead we calculate
                // the values of the arguments to the constructor first, store them
                // in temporary variables, create the object and reload the
                // arguments from the temporaries to avoid the problem.


                LocalVariableGen nodeIteratorTemp =
                    methodGen.addLocalVariable("filter_expr_tmp1",
                                               Util.getJCRefType(NODE_ITERATOR_SIG),
                                               null, null);
                nodeIteratorTemp.setStart(
                        il.append(new ASTORE(nodeIteratorTemp.getIndex())));

                predicate.translate(classGen, methodGen);
                LocalVariableGen filterTemp =
                    methodGen.addLocalVariable("filter_expr_tmp2",
                                  Util.getJCRefType(CURRENT_NODE_LIST_FILTER_SIG),
                                  null, null);
                filterTemp.setStart(il.append(new ASTORE(filterTemp.getIndex())));

                // Create a CurrentNodeListIterator
                il.append(new NEW(cpg.addClass(CURRENT_NODE_LIST_ITERATOR)));
                il.append(DUP);

                // Initialize CurrentNodeListIterator
                nodeIteratorTemp.setEnd(
                        il.append(new ALOAD(nodeIteratorTemp.getIndex())));
                il.append(ICONST_1);
                filterTemp.setEnd(il.append(new ALOAD(filterTemp.getIndex())));
                il.append(methodGen.loadCurrentNode());
                il.append(classGen.loadTranslet());
                il.append(new INVOKESPECIAL(initCNLI));
            }
        }
    }
}

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