Sorting Collections Doubt

[aslika bahini]

Hi,

If, there are two or more elements are same in a list(dvdList). I get different output at different time of execution. Is that how sorting algorithm work in collections?

  GenreSort gs = new GenreSort();
            Collections.sort(dvdList,gs); 
            System.out.println(dvdList);
 
    

Thanks
Saritha
[ September 27, 2008: Message edited by: saritha babu ]

[Henry Wong]

Could you show us the comparator code? Could you show us sample data? Could you show us sample output? Etc...

Obviously, a sorting algorithm that sorts differently, depending on time of day, is *not* how it is supposed to work.

Henry

[aslika bahini]

Could you show us the comparator code? Could you show us sample data? Could you show us sample output? Etc...

Hi Henry,

Here is the Comparator code...

 class GenreSort implements Comparator<DVDInfo>
{
public int compare(DVDInfo one, DVDInfo two)
{
return one.getGenre().compareTo(two.getGenre());
}
}    

first output is:

[Raiders of the Lost Ark action Ford, Harrison
, Patriot Games action Ford, Harrison
, Caddy Shack comedy Murray, Bill
, Lost in Translation comedy Murray, Bill
, Donnie Darko sci-fi Gyllenhall,Jake
, 2001 sci-fi ??
, Star Wars sci-fi Ford, Harrison
]
second output is:

[Patriot Games action Ford, Harrison
,Raiders of the Lost Ark action Ford, Harrison
, Caddy Shack comedy Murray, Bill
, Lost in Translation comedy Murray, Bill
, Donnie Darko sci-fi Gyllenhall,Jake
, 2001 sci-fi ??
, Star Wars sci-fi Ford, Harrison
]

Thank you
Saritha

[Shiraz Choudhary]

Hi Saritha!
I am not sure if i am right, but i am guessing that you are only sorting the collection just by the genre.
The "toString()" method for "DVDInfo" object is this:

return title+" "+genre +" "+leadActor +"\n";
[\CODE]
Now if you add few [B]DVDInfo[/B] objects into a [B]collection[/B] and try to sort the collection just by the [B]genre[/B], like you are doing in the following code:
[CODE]
           GenreSort gs = new GenreSort();
            Collections.sort(dvdList,gs); 
            System.out.println(dvdList);
 
    

then the output you have is sorted by genre.
Look at it again, genre is sorted.

........action..............
........action..............
........comedy..........
........comedy.........
........sci-fi........
........sci-fi........
........sci-fi.......



(in both outputs)

The collection is not sorted by the title so the DVDInfo objects that has the same genre but different titles can switch their order but only within each other.
You will not have comedy or Sci-fi come before action, no matter how many times you run the code.

It would be easy to answer your question if you write all of the code for this program. Like how you are sorting (compareTo or Compare method) the main method etc.

[ September 27, 2008: Message edited by: Shiraz Choudhary ]
[ September 27, 2008: Message edited by: Shiraz Choudhary ]

[aslika bahini]

Hi Shiraz Choudhary,

It would be easy to answer your question if you write all of the code for this program. Like how you are sorting (compareTo or Compare method) the main method etc

Here is the code...
I think I am little confused. I get the same result when I execute this time. The result in book(pg 555) and mine is different. Thanks for the help.

  import java.util.*;
import java.io.*;
class DVDInfo// implements Comparable<DVDInfo>
{
String title;
String genre;
String leadActor;
 
DVDInfo(String t,String g, String a)
{
title = t;
genre = g;
leadActor = a;
}
public String getTitle() {
return title;
}

public String getGenre() {
return genre;
}

public String getLeadActor() {
return leadActor;
}
public String toString()
{
return title +" "+ genre + " " + leadActor + "\n";
}
public int compareTo(DVDInfo d)
{
return title.compareTo(d.getTitle()); //String class implements Comparable interface.
}                                           //Here, title is a String 

}
class GenreSort implements Comparator<DVDInfo>
{
public int compare(DVDInfo one, DVDInfo two)
{
return one.getGenre().compareTo(two.getGenre());
}
}
class ReadDVDInfo
{
ArrayList<DVDInfo>dvdInfoList = new ArrayList<DVDInfo>();
public void populateList()
{
 

try
{
File file = new File("dvdinfo.txt");
FileReader fr = new FileReader(file);
BufferedReader bfr = new BufferedReader(fr);
 
String sentence = bfr.readLine();
           while (sentence != null)
{
 
 ArrayList<String> splitList = splitSentence(sentence);
DVDInfo info = new DVDInfo(splitList.get(0), splitList.get(1), splitList.get(2));
dvdInfoList.add(info);
                 
sentence = bfr.readLine();
}
            
 
fr.close();
 
}catch(IOException e)        
{
e.printStackTrace();
}
}
 

public ArrayList<String> splitSentence(String sentence)
{
ArrayList<String> al = new ArrayList<String>();   
String[] tokens = sentence.split("/");
for(int i = 0; i<tokens.length;i++)
{
al.add(tokens[i]);
}
return al;
 
}

}
 
public class TestDVD {
public static void main(String args[])
{
ReadDVDInfo readObj = new ReadDVDInfo();
readObj.populateList();
//Collections.sort(readObj.dvdInfoList);
//System.out.println("Output sorted by title");
//System.out.println(readObj.dvdInfoList);
GenreSort gs = new GenreSort();
Collections.sort(readObj.dvdInfoList,gs);
System.out.println(readObj.dvdInfoList);

}
 
}
  

Thanks
Saritha