This program sorts a set of item by comparing their descriptions : Comparable « Collections Data Structure « Java

1. Java
2. Collections Data Structure
3. Comparable

This program sorts a set of item by comparing their descriptions

 
/*
   This program is a part of the companion code for Core Java 8th ed.
   (http://horstmann.com/corejava)

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

/**
   @version 1.10 2004-08-02
   @author Cay Horstmann
*/

import java.util.Comparator;
import java.util.SortedSet;
import java.util.TreeSet;

/**
   This program sorts a set of item by comparing
   their descriptions.
*/
public class TreeSetTest
{  
   public static void main(String[] args)
   {  
      SortedSet<Item> parts = new TreeSet<Item>();
      parts.add(new Item("Toaster", 1234));
      parts.add(new Item("Widget", 4562));
      parts.add(new Item("Modem", 9912));
      System.out.println(parts);

      SortedSet<Item> sortByDescription = new TreeSet<Item>(new
         Comparator<Item>()
         {  
            public int compare(Item a, Item b)
            {  
               String descrA = a.getDescription();
               String descrB = b.getDescription();
               return descrA.compareTo(descrB);
            }
         });

      sortByDescription.addAll(parts);
      System.out.println(sortByDescription);
   }
}

/**
   An item with a description and a part number.
*/
class Item implements Comparable<Item>
{ 
   /**
      Constructs an item.
      @param aDescription the item's description
      @param aPartNumber the item's part number
   */
   public Item(String aDescription, int aPartNumber)
   {  
      description = aDescription;
      partNumber = aPartNumber;
   }

   /**
      Gets the description of this item.
      @return the description
   */
   public String getDescription()
   {  
      return description;
   }

   public String toString()
   {  
      return "[descripion=" + description
         + ", partNumber=" + partNumber + "]";
   }

   public boolean equals(Object otherObject)
   {  
      if (this == otherObject) return true;
      if (otherObject == null) return false;
      if (getClass() != otherObject.getClass()) return false;
      Item other = (Item) otherObject;
      return description.equals(other.description)
         && partNumber == other.partNumber;
   }

   public int hashCode()
   {  
      return 13 * description.hashCode() + 17 * partNumber;
   }

   public int compareTo(Item other)
   {  
      return partNumber - other.partNumber;
   }

   private String description;
   private int partNumber;
}

   
  

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