Sorting a list in Java the same way, ids appear in an array

Question

I have an array with ids

  [2,3,1]

From an external rest Service, I'll get a List with UserObjects. These userObjects contains userids (1 or 2 or 3)

I now would like to sort the list in the same order, The userids appear in my array. Maybe it's helpful to say that I am able to use guava (v15) in my code. Thanks.

Answer 1

int[] ids = ...
List<UserObject> userObjects = ...
Collections.sort(userObjects, new Comparator<UserObject>() {
  public int compare(UserObject a, UserObject b) {
    return Ints.compare(
        Ints.indexOf(ids, a.getId()),
        Ints.indexOf(ids, b.getId()));
  }
});

Answer 2

You can use Collections.sort(List,Comparator), with a comparator like this:

class MyComp implements Comparator<UserObject> {

    private int[] ref;

    public MyComp(int [] reference) {
        this.ref=reference;
    }

    public compare(UserObject o1, UserObjects o2) {
        return Ints.indexOf(ref,o1.id) - Ints.indexOf(ref,o2.id);
    }
}

Answer 3

Arrays.sort is your friend : http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#sort(short[])

Or if you want to sort a collection of complex types, make sure the complex type (user?) implements comparable and compareTo.

Or more likely in this, you'll need to supply a custom comparator, which allows sorting by in different orders like this.