mathoperator.java

来自「OpenJMS是一个开源的Java Message Service API 1.」· Java 代码 · 共 115 行

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 */

package org.exolab.jms.selector;

import javax.jms.Message;


/**
 * This class is the base class for all expressions that are numeric binary
 * operators. These return a numeric result when evaluated, or null
 * if the result is undefined.
 *
 * @version     $Revision: 1.1 $ $Date: 2004/11/26 01:50:44 $
 * @author      <a href="mailto:[e-mail]">Tim Anderson</a>
 * @see         Expression
 * @see         SNumber
 */
abstract class MathOperator extends BinaryOperator {

    /**
     * Construct a new <code>MathOperator</code>
     *
     * @param operator the operator
     * @param lhs the left hand side of the expression
     * @param rhs the right hand side of the expression
     */
    protected MathOperator(final String operator, final Expression lhs,
                           final Expression rhs) {
        super(operator, lhs, rhs);
    }

    /**
     * Evaluate the expression
     *
     * @param msg the message to evaluate this expression against
     * @return the result of expression
     * @throws TypeMismatchException if the result of the left or right
     * hand expressions are not numeric
     */
    public final SObject evaluate(final Message msg)
        throws TypeMismatchException {

        SNumber result = null;
        SNumber lhs = TypeCaster.castToNumber(left().evaluate(msg), context());
        if (lhs != null) {
            SNumber rhs = TypeCaster.castToNumber(right().evaluate(msg),
                context());
            if (rhs != null) {
                result = evaluate(lhs, rhs);
            }
        }
        return result;
    }

    /**
     * Evaluate the expression
     *
     * @param lhs the left hand side of the expression
     * @param rhs the right hand side of the expression
     * @return the result of expression
     */
    protected abstract SNumber evaluate(final SNumber lhs, final SNumber rhs);

    /**
     * The context of the expression, for error reporting purposes
     *
     * @return the context of the expression
     */
    private final String context() {
        return "operator " + operator();
    }

} //-- MathOperator