Commons JXPath example source code file (CoreOperation.java)

This example Commons JXPath source code file (CoreOperation.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

add_precedence, and_precedence, compare_precedence, coreoperation, coreoperation, object, object, operation, or_precedence, relational_expr_precedence, string, string, stringbuffer, stringbuffer

The Commons JXPath CoreOperation.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 org.apache.commons.jxpath.ri.EvalContext;

/**
 * The common subclass for tree elements representing core operations like "+",
 * "- ", "*" etc.
 *
 * @author Dmitri Plotnikov
 * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
 */
public abstract class CoreOperation extends Operation {

    /** or precedence */
    protected static final int OR_PRECEDENCE = 0;
    /** and precedence */
    protected static final int AND_PRECEDENCE = 1;
    /** compare precedence */
    protected static final int COMPARE_PRECEDENCE = 2;
    /** relational expression precedence */
    protected static final int RELATIONAL_EXPR_PRECEDENCE = 3;
    /** add/subtract precedence */
    protected static final int ADD_PRECEDENCE = 4;
    /** multiply/divide/mod precedence */
    protected static final int MULTIPLY_PRECEDENCE = 5;
    /** negate precedence */
    protected static final int NEGATE_PRECEDENCE = 6;
    /** union precedence */
    protected static final int UNION_PRECEDENCE = 7;

    /**
     * Create a new CoreOperation.
     * @param args Expression[]
     */
    public CoreOperation(Expression[] args) {
        super(args);
    }

    public Object compute(EvalContext context) {
        return computeValue(context);
    }

    public abstract Object computeValue(EvalContext context);

    /**
     * Returns the XPath symbol for this operation, e.g. "+", "div", etc.
     * @return String symbol
     */
    public abstract String getSymbol();

    /**
     * Returns true if the operation is not sensitive to the order of arguments,
     * e.g. "=", "and" etc, and false if it is, e.g. "<=", "div".
     * @return boolean
     */
    protected abstract boolean isSymmetric();

    /**
     * Computes the precedence of the operation.
     * @return int precedence
     */
    protected abstract int getPrecedence();

    public String toString() {
        if (args.length == 1) {
            return getSymbol() + parenthesize(args[0], false);
        }
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < args.length; i++) {
            if (i > 0) {
                buffer.append(' ');
                buffer.append(getSymbol());
                buffer.append(' ');
            }
            buffer.append(parenthesize(args[i], i == 0));
        }
        return buffer.toString();
    }

    /**
     * Wrap an expression in parens if necessary.
     * @param expression other Expression
     * @param left whether <code>expression is left of this one.
     * @return String
     */
    private String parenthesize(Expression expression, boolean left) {
        String s = expression.toString();
        if (!(expression instanceof CoreOperation)) {
            return s;
        }
        int compared = getPrecedence() - ((CoreOperation) expression).getPrecedence();

        if (compared < 0) {
            return s;
        }
        if (compared == 0 && (isSymmetric() || left)) {
            return s;
        }
        return '(' + s + ')';
    }
}