Commons JXPath example source code file (CoreOperationRelationalExpression.java)

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

Java - Commons JXPath tags/keywords

collection, collection, coreoperation, coreoperationrelationalexpression, evalcontext, hashset, initialcontext, initialcontext, iterator, iterator, object, object, relational_expr_precedence, selfcontext, util

The Commons JXPath CoreOperationRelationalExpression.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.commons.jxpath.ri.compiler;

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

import org.apache.commons.jxpath.ri.EvalContext;
import org.apache.commons.jxpath.ri.InfoSetUtil;
import org.apache.commons.jxpath.ri.axes.InitialContext;
import org.apache.commons.jxpath.ri.axes.SelfContext;

/**
 * Base implementation of Expression for the operations ">", ">=", "<", "<=".
 * @since JXPath 1.3
 *
 * @author Matt Benson
 * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
 */
public abstract class CoreOperationRelationalExpression extends CoreOperation {

    /**
     * Create a new CoreOperationRelationalExpression.
     * @param args arguments
     */
    protected CoreOperationRelationalExpression(Expression[] args) {
        super(args);
    }

    public final Object computeValue(EvalContext context) {
        return compute(args[0].compute(context), args[1].compute(context))
                ? Boolean.TRUE : Boolean.FALSE;
    }

    protected final int getPrecedence() {
        return RELATIONAL_EXPR_PRECEDENCE;
    }

    protected final boolean isSymmetric() {
        return false;
    }

    /**
     * Template method for subclasses to evaluate the result of a comparison.
     * @param compare result of comparison to evaluate
     * @return ultimate operation success/failure
     */
    protected abstract boolean evaluateCompare(int compare);

    /**
     * Compare left to right.
     * @param left left operand
     * @param right right operand
     * @return operation success/failure
     */
    private boolean compute(Object left, Object right) {
        left = reduce(left);
        right = reduce(right);

        if (left instanceof InitialContext) {
            ((InitialContext) left).reset();
        }
        if (right instanceof InitialContext) {
            ((InitialContext) right).reset();
        }
        if (left instanceof Iterator && right instanceof Iterator) {
            return findMatch((Iterator) left, (Iterator) right);
        }
        if (left instanceof Iterator) {
            return containsMatch((Iterator) left, right);
        }
        if (right instanceof Iterator) {
            return containsMatch((Iterator) right, left);
        }
        double ld = InfoSetUtil.doubleValue(left);
        if (Double.isNaN(ld)) {
            return false;
        }
        double rd = InfoSetUtil.doubleValue(right);
        if (Double.isNaN(rd)) {
            return false;
        }
        return evaluateCompare(ld == rd ? 0 : ld < rd ? -1 : 1);
    }

    /**
     * Reduce an operand for comparison.
     * @param o Object to reduce
     * @return reduced operand
     */
    private Object reduce(Object o) {
        if (o instanceof SelfContext) {
            o = ((EvalContext) o).getSingleNodePointer();
        }
        if (o instanceof Collection) {
            o = ((Collection) o).iterator();
        }
        return o;
    }

    /**
     * Learn whether any element returned from an Iterator matches a given value.
     * @param it Iterator
     * @param value to look for
     * @return whether a match was found
     */
    private boolean containsMatch(Iterator it, Object value) {
        while (it.hasNext()) {
            Object element = it.next();
            if (compute(element, value)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Learn whether there is an intersection between two Iterators.
     * @param lit left Iterator
     * @param rit right Iterator
     * @return whether a match was found
     */
    private boolean findMatch(Iterator lit, Iterator rit) {
        HashSet left = new HashSet();
        while (lit.hasNext()) {
            left.add(lit.next());
        }
        while (rit.hasNext()) {
            if (containsMatch(left.iterator(), rit.next())) {
                return true;
            }
        }
        return false;
    }

}