constantexpression.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>ConstantExpression</code> represents a constant expression.</p>
  *
  * <p> In other words, {@link #evaluate} returns a value independent of the context. </p>
  *
  * @author <a href="mailto:[e-mail]">James Strachan</a>
  * @version $Revision: 1.6 $
  */
public class ConstantExpression implements Expression {

    /** The value of this expression */
    private Object value;
    
    /** Base constructor
     */
    public ConstantExpression() {
    }
    
    /** 
      * Convenience constructor sets <code>value</code> property.
      * @param value the Object which is the constant value for this expression
      */
    public ConstantExpression(Object value) {
        this.value = value;
    }
    
    /** 
      * Evaluate expression against given context.
      *
      * @param context evaluate expression against this context
      * @return current value of <code>value</code> property  
      */
    public Object evaluate(Context context) {
        return value;
    }
    
    /**
     * Do nothing
     * @see org.apache.commons.betwixt.expression.Expression
     */
    public void update(Context context, String newValue) {
        // do nothing
    }

    /** 
     * Gets the constant value of this expression 
     * @return this expression's constant value 
     */
    public Object getValue() {
        return value;
    }
    
    /**  
     * Sets the constant value of this expression 
     * @param value the constant value for this expression
     */
    public void setValue(Object value) {
        this.value = value;
    }
    
    /**
     * Returns something useful for logging
     * @return something useful for logging
     */
    public String toString() {
        return "ConstantExpression [value=" + value + "]";
    }
}