guava RangeMap

By traviscj

- 1 minutes read - 158 words

We had some code like this:

NavigableMap<Double, Integer> PRIORITY_MULTIPLIERS = new TreeMap<Double, Integer>() {{ "{{ " }}
  put(LOW_THRESHOLD, 1);    // (20k..40k)  => 1
  put(MEDIUM_THRESHOLD, 2); // [40k..100k) => 2
  put(HIGH_THRESHOLD, 3);   // [100k..+∞)  => 3
}};

Integer getPriorityMultiplier(Double v) {
  if (v < LOW_THRESHOLD) {
    return 0;
  }
  return PRIORITY_MULTIPLIERS.floorEntry(v).getValue()
}

I replaced with a [RangeMap][RangeMap] that uses [Range][Range] instances as keys: [RangeMap]: https://google.github.io/guava/releases/16.0/api/docs/com/google/common/collect/RangeMap.html [Range]: https://google.github.io/guava/releases/16.0/api/docs/com/google/common/collect/Range.html

RangeMap<Double, Integer> PRIORITY_MULTIPLIERS = ImmutableRangeMap.<Double, Long>builder()
      .put(Range.lessThan(LOW_THRESHOLD), 0)
      .put(Range.closedOpen(LOW_THRESHOLD, MEDIUM_THRESHOLD), 1)
      .put(Range.closedOpen(MEDIUM_THRESHOLD, HIGH_THRESHOLD), 2)
      .put(Range.atLeast(HIGH_THRESHOLD), 3)
      .build();
Integer getPriorityMultiplier(Double v) {
  return rangePriorityMultipliers.get(v);
}

Advantages here being:

  1. ImmutableRangeMap explicitly checks for overlapping ranges, so specifying Range.atMost for the first range would fail at the time of instantiation.

  2. Puts declaration & endpoint behavior (open vs closed) together, instead of partly in the Map declaration and partly in the map.floorEntry call.

  3. Simple to test that entire range is covered:

    @Test public void multipliersForEntireRange() {
  Set<Range<Double>> ranges = PRIORITY_MULTIPLIERS.asMapOfRanges().keySet();
  ImmutableRangeSet<Double> rangeSet = ImmutableRangeSet.copyOf(ranges);
  assertThat(rangeSet.encloses(Range.all())).isTrue();
}