Java – list sorting challenges

Suppose I have

final Iterable<String> unsorted = asList("FOO","BAR","PREFA","ZOO","PREFZ","PREFOO");

What can I do to convert this unordered list to:

[PREFZ,PREFA,BAR,FOO,PREFOO,ZOO]

(list starting with known values that must appear first (here "prefa" and "prefz"), the rest are sorted alphabetically)

I think there are some useful classes in guava that can do this (ordering, predictions...), but I haven't found a solution yet

Solution

You mentioned guava in particular; Together with Sylvain M's answer, this is another way (more like an academic exercise and a demonstration of guava flexibility than any other way)

// List is not efficient here; for large problems,something like SkipList 
// is more suitable
private static final List<String> KNowN_INDEXES = asList("PREFZ","PREFA");

private static final Function<Object,Integer> POSITION_IN_KNowN_INDEXES 
    = new Function<Object,Integer>() {
  public Integer apply(Object in) {
     int index = KNowN_INDEXES.indexOf(in);
     return index == -1 ? null : index;
  }     
};


...


List<String> values = asList("FOO","PREFOO");

Collections.sort(values,Ordering.natural().nullsLast().onResultOf(POSITION_IN_KNowN_INDEXES).compound(Ordering.natural())
);

In other words, press list Indexof() returns the natural order of integers, and then breaks the relationship with the natural order of the object itself

It may be messy, but it's interesting