/* * Copyright (c) 2002-2003 by OpenSymphony * All rights reserved. */package com.opensymphony.workflow.query;import java.io.Serializable;/** * Abstract base class for expressions used in a workflow query. * Expressions can be negate and/or nested. The default is not negate. * <p></p> * Expressions which are supported by all stores are {@link FieldExpression} and {@link NestedExpression}. * <p></p> * Store specific expressions like XPathExpression can be added. * * @author Christine Zimmermann */public abstract class Expression implements Serializable {    //~ Instance fields ////////////////////////////////////////////////////////    protected boolean negate = false;    //~ Constructors ///////////////////////////////////////////////////////////    protected Expression() {    }    //~ Methods ////////////////////////////////////////////////////////////////    public boolean isNegate() {        return negate;    }    abstract public boolean isNested();}