BasicSorter.java

/*
** Module   : BasicSorter.java
** Abstract : Directional comparator for Comparables
**
** Copyright (c) 2004-2017, Golden Code Development Corporation.
**
** -#- -I- --Date-- -T- --JPRM-- ----------------Description-----------------
** 001 ECF 20080708 ADD  @39078  Created initial version. Abstracted as a base
**                               class from DataSorter. Needed to handle non-
**                               BaseDataType Comparables.
*/
/*
** This program is free software: you can redistribute it and/or modify
** it under the terms of the GNU Affero General Public License as
** published by the Free Software Foundation, either version 3 of the
** License, or (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU Affero General Public License for more details.
**
** You may find a copy of the GNU Affero GPL version 3 at the following
** location: https://www.gnu.org/licenses/agpl-3.0.en.html
** 
** Additional terms under GNU Affero GPL version 3 section 7:
** 
**   Under Section 7 of the GNU Affero GPL version 3, the following additional
**   terms apply to the works covered under the License.  These additional terms
**   are non-permissive additional terms allowed under Section 7 of the GNU
**   Affero GPL version 3 and may not be removed by you.
** 
**   0. Attribution Requirement.
** 
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*/

package com.goldencode.p2j.persist;

import java.io.*;
import java.util.*;

/**
 * An implementation of <code>Comparator</code>, used to sort instances of
 * <code>Comparable</code>s in ascending or descending order.  Direction of
 * the sort is specified upon construction.
 * 
 * @param   <T>
 *          A type which extends/implements Comparable
 */
public class BasicSorter<T extends Comparable>
implements Comparator<T>,
           Serializable
{
   /** Multiplier used to adjust (possibly invert) sorting */
   private final int direction;
   
   /**
    * Constructor which stores the sort direction.
    *
    * @param   ascending
    *          <code>true</code> if sort should be ascending;
    *          <code>false</code> if it should be descending.
    */
   protected BasicSorter(boolean ascending)
   {
      this.direction = (ascending ? 1 : -1);
   }
   
   /**
    * Compare two <code>Comparable</code> instances to determine relative
    * sort order.  The comparison uses the natural order of the objects,
    * except that unknown value always sorts high in an ascending sort.  The
    * result is inverted for descending sorts (meaning unknown value sorts low
    * in a descending sort.
    * 
    * @param   d1
    *          First value to compare.  Must not be <code>null</code>.
    * @param   d2
    *          Second value to compare.  Must not be <code>null</code>.
    * 
    * @return  Positive value if <code>d1</code> &gt; <code>d2</code>;
    *          negative value if <code>d1</code> &lt; <code>d2</code>;
    *          <code>0</code> if <code>d1</code> and <code>d2</code> sort
    *          equivalently.
    */
   public int compare(T d1, T d2)
   {
      int result = d1.compareTo(d2);
      
      return (result * direction);
   }
   
   /**
    * Calculate a hash code for this object.
    * 
    * @return  Hash code.
    */
   public int hashCode()
   {
      int result = 17;
      result = 37 * result + direction;
      
      return result;
   }

   /**
    * Test for equality between this comparator and another.  Equality means
    * either both comparators represent the same object instance in memory,
    * or that both comparators are instances of this class and sort in the
    * same direction.
    * 
    * @return  <code>true</code> if objects are equal, else
    *          <code>false</code>.
    */
   public boolean equals(Object o)
   {
      if (this == o)
      {
         return true;
      }
      
      if (!(o instanceof BasicSorter))
      {
         return false;
      }
      
      BasicSorter<T> that = (BasicSorter<T>) o;
      
      return (this.direction == that.direction);
   }
   
   /**
    * Report the direction in which this sorter sorts its data.
    * 
    * @return  1 if ascending or -1 if descending.
    */
   protected int getDirection()
   {
      return direction;
   }
}