emptyexpression.java

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/*
 * Copyright 2001-2004 The Apache Software Foundation.
 * 
 * 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 org.apache.commons.betwixt.expression;

/** <p><code>EmptyExpression</code> returns the same value as is passed in. </p>
  * 
  * <p> See {@link #evaluate}. </p>
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.6 $
  */
public class EmptyExpression implements Expression {
    
    /** Don't need more than one <code>EmptyExpression</code>*/
    private static final EmptyExpression singleton = new EmptyExpression();
    
    /**
     * Gets the singleton instance.
     * @return the EmptyExpression singleton. 
     */
    public static EmptyExpression getInstance() {
        return singleton;
    }
    
    /** Should this be private?
     */
    public EmptyExpression() {
    }
    
    /** Return the bean we're evaluating.
     * @see org.apache.commons.betwixt.expression.Expression
     */ 
    public Object evaluate(Context context) {
        return context.getBean();
    }
    
    /** Do nothing
     * @see org.apache.commons.betwixt.expression.Expression
     */ 
    public void update(Context context, String newValue) {
        // do nothing
    }
    
    /**
     * Return something useful for logging.
     * @return short name for this class
     */
    public String toString() {
        return "EmptyExpression";
    }
    
}