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This is a plugin to Madura Objects. It provides a rules/constraint engine to assist with validation, deriving new values from user inputs (eg total of invoices entered on this customer) an manipulating metadata (eg because the amount is above X we make some field readonly). Note that the Java that is using the monitored objects is quite unaware of the rules layer implemented here. That means you can change rules without having to go back to your Java code, and it also means you don't have to wonder if everything implemented the same rules. Anything using that Java object has the rules (unless you turn them all off).

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/*******************************************************************************
 * Copyright (c)2014 Prometheus Consulting
 *
 * Licensed 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 nz.co.senanque.rulesparser;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;



/**
 * Encapsulates an element which most of the other abstractions
 * implement. Also contains the Element factory.
 * 
 * The element factory is not particularly efficient (string compares)
 * But it isn't run very often, this is the parser code not the runtime code.
 * 
 * @author Roger Parkinson
 * @version $Revision: 1.4 $
 */
public abstract class ExpressionElement
{
    private static final Logger log = LoggerFactory.getLogger(ExpressionElement.class);
    protected static final String SPACES = "        ";
	private final String m_value;
	private boolean m_used;
	/**
	 * Constructor for ParsedElement1.
	 */
	public ExpressionElement(String value)
	{
		m_value = value;
	}
	public boolean isAssign()
	{
		return false;
	}
	
	/**
	 * Returns the value.
	 * @return String
	 */
	public final String getValue()
	{
		return m_value;
	}
	
    public final static ExpressionElement parsedElementFactory(FunctionDescriptor od)
    {
        return new Operator(od);
    }
    public boolean isUsed()
    {
        return m_used;
    }
    public void setUsed(boolean used)
    {
        m_used = used;
    }
    public abstract Class getTypeAsClass();
    
    public String toString()
    {
        if (!log.isDebugEnabled())
        {
            return "";
        }
        return (isUsed()?" used":"");
    }

}