variableexpression.java

JAVA 文章管理系统源码

/*
 * 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>VariableExpression</code> represents a variable expression such as 
  * <code>$foo</code> which returns the value of the given variable.</p>
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.6 $
  */
public class VariableExpression implements Expression {

    /** The variable name */
    private String variableName;
    
    /** Base constructor */
    public VariableExpression() {
    }
    
    /** 
     * Convenience constructor sets <code>VariableName</code> property 
     * @param variableName the name of the context variable 
     * whose value will be returned by an evaluation 
     */
    public VariableExpression(String variableName) {
        this.variableName = variableName;
    }
    
    /** Return the value of a context variable.
      *
      * @param context evaluate against this context
      * @return the value of the context variable named by the <code>VariableName</code> property
      */
    public Object evaluate(Context context) {
        return context.getVariable( variableName );
    }
    
    /** 
     * Gets the variable name 
     * @return the name of the context variable whose value will be returned by an evaluation
     */
    public String getVariableName() {
        return variableName;
    }
    
    /** 
     * Sets the variable name 
     * @param variableName the name of the context variable 
     * whose value will be returned by an evaluation
     */
    public void setVariableName(String variableName) {
        this.variableName = variableName;
    }
    
    /**
     * Do nothing
     * @see org.apache.commons.betwixt.expression.Expression
     */
    public void update(Context context, String newValue) {
        // do nothing
    }

    /**
     * Returns something useful for logging
     * @return something useful for logging
     */
    public String toString() {
        return "VariableExpression [variable name=" + variableName + "]";
    }
}