Sorting: How to create a particular custom order, then alphabetic sort in java

Question

I have an Enum with around 70 fields.

I want 10 of them to be displayed in a particular order, then I want the rest to be displayed alphabetically using a Comparator. I have tried many things, but I can't get it to work.

Here is a sample enum with reduces attributes I want Picard, Worf and William to display first, then the rest alphabetically

I cannot use any third libraries. It must be java core. So if you want to provide guava answers, or apache commons answer, please do so in addition to java core.

public enum StarTrek {

    JeanLucPicard("Picard"),
    GeordiLaForge("Geordi"),
    DiannaTroi("Dianna"),
    Worf("Worf"),
    WilliamRiker("William"),
    Q("Q");

    private String label;

    StarTrek(String label) { this.label = label; }

    @Override public String toString() { return label; }
}

    List<StarTrek> specificOrder = Arrays.asList(StarTrek.JeanLucPicard, StarTrek.Worf, StarTrek.WilliamRiker);

    Comparator<StarTrek> comp = new Comparator<StarTrek>() {
            @Override
            public int compare(StarTrek o1, StarTrek o2) {
                //TODO: loop through the specific order, and display those first, then for the rest, go alphabetic
                return 0;
            }
    };

    List<StarTrek> all = Arrays.asList(StarTrek.values());
    Collections.sort(all, comp);

Answer 1

It is bad design to place additional data in your enum just for the purposes of displaying in a particular order. Instead, place all that logic in your Comparator, as shown below:

public class StarTrekSorter implements Comparator<StarTrek> {

  private static final List<StarTrek> ORDERED_ENTRIES = Arrays.asList(
      StarTrek.JeanLucPicard, StarTrek.Worf, StarTrek.WilliamRiker);

  @Override
  public int compare(StarTrek o1, StarTrek o2) {
    if (ORDERED_ENTRIES.contains(o1) && ORDERED_ENTRIES.contains(o2)) {
      // Both objects are in our ordered list. Compare them by
      // their position in the list
      return ORDERED_ENTRIES.indexOf(o1) - ORDERED_ENTRIES.indexOf(o2);
    }

    if (ORDERED_ENTRIES.contains(o1)) {
      // o1 is in the ordered list, but o2 isn't. o1 is smaller (i.e. first)
      return -1;
    }

    if (ORDERED_ENTRIES.contains(o2)) {
      // o2 is in the ordered list, but o1 isn't. o2 is smaller (i.e. first)
      return 1;
    }

    return o1.toString().compareTo(o2.toString());
  }
}

Now, you can just sort:

public static void main(String[] args) {

  List<StarTrek> cast = Arrays.asList(StarTrek.values());

  Collections.sort(cast, new StarTrekSorter());

  for (StarTrek trek : cast) {
    System.out.println(trek);
  }  
}

which prints

Picard
Worf
William
Dianna
Geordi
Q