fastest way to sort a list in Java

Question

I have the following code in Java:

   public  class ServerInfo {
    int serverId;
    int serverDataRate;
    public ServerInfo(int serverId, int serverDataRate) {
        this.serverId = serverId;
        this.serverDataRate = serverDataRate;
    }
    public int getServerId() {
        return serverId;
    }
    public double getServerDataRate() {
        return serverDataRate;
    }
       public String toString(){
            return serverId + ":" + serverDataRate;
        }
    }    

    public class ServerInfoComparator implements Comparator<ServerInfo> {

    @Override
    public int compare(ServerInfo o1, ServerInfo o2) {
          double datarate1=o1.getServerDataRate();
          double datarate2=o2.getServerDataRate();

          if(datarate1>datarate2)
              return -1;
          else if(datarate1<datarate2)
              return +1;
          else
              return 0;
    }           
}

   public class Sample {
    List<ServerInfo> listOfServers= new ArrayList<ServerInfo>();

    public void insertIntoList(){

        listOfServers.add( new ServerInfo(0,256));
        listOfServers.add( new ServerInfo(1,270));
        listOfServers.add( new ServerInfo(2,256));
        listOfServers.add( new ServerInfo(3,290));
        listOfServers.add( new ServerInfo(4,300));
        listOfServers.add( new ServerInfo(5,300));
        listOfServers.add( new ServerInfo(6,256));
        listOfServers.add( new ServerInfo(7,265));
        listOfServers.add( new ServerInfo(8,289));
        listOfServers.add( new ServerInfo(9,310));  
    }

    public static void main( String[] args){
        Sample s = new Sample();
        s.insertIntoList();
        ServerInfoComparator com  = new ServerInfoComparator();
        Collections.sort(s.listOfServers,com);

        for( ServerInfo server: s.listOfServers){
            System.out.println(server);
        }           
    }
}

I am using the above code to sort the elements in descending order based on the serverDataRate. Here the sample set is quite small supposing I have a larger sample set of 100 elements in the list and the code had to be executed every 5-10 seconds. Is this the fastest way to sort the list or is there a faster method I am not aware of?

Answer 1

I changed your test

private final List<ServerInfo> listOfServers = new ArrayList<ServerInfo>();

public void insertIntoList() {
    for (int i = 0; i < 1000000; i++)
        listOfServers.add(new ServerInfo(i, (int) (200 + Math.random() * 200)));
}

public static void main(String[] args) {
    MyApp s = new MyApp();
    s.insertIntoList();
    ServerInfoComparator com = new ServerInfoComparator();
    long start = System.nanoTime();
    Collections.sort(s.listOfServers, com);
    long time = System.nanoTime() - start;
    System.out.printf("Sorting %,d took %.3f seconds%n", s.listOfServers.size(), time/1e9);

    for (ServerInfo server : s.listOfServers) {
//    System.out.println(server);
    }
}

and it prints

Sorting 1,000,000 took 0.438 seconds

That's quite a bit faster ;)

BTW: I changed the double fields to be int.

Answer 2

100 elements isn't a large set unless your comparison step is really heavy (doesn't seem like it). 100 elements will get sorted extremely fast in any slightly modern machine.

That being said, I think your approach is pretty close to standard, and I wouldn't worry about trying to optimize it unless you really end up needing it.

Early optimization is the father of many screw ups (assumptions being the mother).