expression.java

UML设计测试工具

/*
 * USE - UML based specification environment
 * Copyright (C) 1999-2004 Mark Richters, University of Bremen
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/* $ProjectHeader: use 2-3-0-release.1 Mon, 12 Sep 2005 20:18:33 +0200 green $ */

package org.tzi.use.uml.ocl.expr;

import org.tzi.use.uml.ocl.type.Type;
import org.tzi.use.uml.ocl.value.Value;

/**
 * Abstract base class of all expressions.
 *
 * @version     $ProjectVersion: 2-3-0-release.1 $
 * @author  Mark Richters
 */
public abstract class Expression {
    private Type fType;     // result type
    private boolean fIsPre = false; // marked "@pre"?
    
    protected Expression(Type t) {
        fType = t;
    }

    /**
     * Returns the result type of the expression.
     */
    public Type type() {
        return fType;
    }

    /**
     * Evaluates the expression and returns a result value.
     */
    public abstract Value eval(EvalContext ctx);

    /**
     * Returns true if this expression has been marked "@pre".
     */
    public boolean isPre() {
        return fIsPre;
    }

    /**
     * Mark this expression with "@pre".
     */
    public void setIsPre() {
        fIsPre = true;
    }

    /**
     * Returns the string "@pre" if this expression has the @pre
     * modifier, otherwise returns "".
     */
    protected String atPre() {
        return fIsPre ? "@pre" : "";
    }

    /**
     * Every expression can print itself.
     */
    public abstract String toString();

    /**
     * Makes sure this is a boolean expression.
     *
     * @exception ExpInvalidException not a boolean expression
     */
    public void assertBoolean() throws ExpInvalidException {
        if (! fType.isBoolean() )
            throw new ExpInvalidException("Boolean expression expected, " + 
                                          "found expression of type `" + this.toString() + "'.");
    }

    /** 
     * Sets the result type explicitly. Use this in subclasses when
     * the result type is complex to determine and cannot easily be
     * passed to the superclass constructor.  
     */
    protected void setResultType(Type t) {
        fType = t;
    }
}