cachevalue.java

实现数据库的storage manager 功能

/*
 * Copyright (c) 2000-2004, Rickard C鰏ter, Martin Svensson
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 * Redistributions of source code must retain the above copyright notice, 
 * this list of conditions and the following disclaimer. 
 * Redistributions in binary form must reproduce the above copyright notice, 
 * this list of conditions and the following disclaimer in the documentation 
 * and/or other materials provided with the distribution. 
 * Neither the name of SICS nor the names of its contributors 
 * may be used to endorse or promote products derived from this software 
 * without specific prior written permission. 
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 *
 *
 */

package com.mellowtech.disc;

public class CacheValue{
  Object value = null;
  boolean dirty = false;

  public CacheValue(Object value){
    this.value = value;
    this.dirty = false;
  }

  /**
   * Return true if the value has changed since it was added to cache.
   *
   * @return a value of type 'boolean'
   */
  public boolean isDirty(){
    return dirty;
  }

  /**
   * Mark this value as changed from entering the cache.
   *
   */
  public void setDirty(){
    dirty = true;
  }

  public void setDirty(boolean dirty){
    this.dirty = dirty;
  }

  /**
   * Get the value. If the isDirty returns false it should be safe
   * to do nothing with the value, i.e. it has not changed since
   * it entered the cache.
   * @return a value of type 'Object'
   */
  public Object getValue(){
    return value;
  }

  /**
   * Set the value and keep the dirty bit as is
   */
  public void setValue(Object value){
    this.value = value;
  }

  
  /**
   * Set the value and set the the dirty bit to false
   */
  public void setAndRestore(Object value){
    this.value = value;
    dirty = false;
  }
}