This is not just an Android thing, the Java SDK has the same recommendation: Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like TreeSet, TreeMap). In order for the data structure to serialize successfully, the comparator (if provided) … Read more
If you don’t want to add a dependency on Guava (per Michael’s answer) then this comparator is equivalent: private static Comparator<String> ALPHABETICAL_ORDER = new Comparator<String>() { public int compare(String str1, String str2) { int res = String.CASE_INSENSITIVE_ORDER.compare(str1, str2); if (res == 0) { res = str1.compareTo(str2); } return res; } }; Collections.sort(list, ALPHABETICAL_ORDER); And I … Read more
Simply changing public int compare(Dog d, Dog d1) { return d.age – d1.age; } to public int compare(Dog d, Dog d1) { return d1.age – d.age; } should sort them in the reverse order of age if that is what you are looking for. Update: @Arian is right in his comments, one of the accepted … Read more
LIKE allows partial matching / use of wildcards, while = checks for exact matches. For example SELECT * FROM test WHERE field LIKE ‘%oom’; Will return rows where field value is any of the following: Zoom, Boom, Loom, Groom
[…] How should Java Comparator class be declared to sort the arrays by their first elements in decreasing order […] Here’s a complete example using Java 8: import java.util.*; public class Test { public static void main(String args[]) { int[][] twoDim = { {1, 2}, {3, 7}, {8, 9}, {4, 2}, {5, 3} }; Arrays.sort(twoDim, … Read more
The exception (whatever it was) was caught by catch (Exception e). You didn’t log this exception, so you don’t know what it was. You should log it somehow so you know what really happened. The problem occurs when you return -1. This allows for the possibility of inconsistent ordering, which Java’s current sorting algorithm sometimes … Read more
You may write your own comparator public class ExampleComparator implements Comparator<String> { public int compare(String obj1, String obj2) { if (obj1 == obj2) { return 0; } if (obj1 == null) { return -1; } if (obj2 == null) { return 1; } return obj1.compareTo(obj2); } }
Guava is more elegant: return ComparisonChain.start() .compare(d1.weight, d2.weight) .compare(d1.age, d2.age) .compare(d1.name, d2.name) .result(); Apache commons-lang has a similar construct, CompareToBuilder.
Comparator#compareTo returns an int; while getTime is obviously long. It would be nicer written like this: .sort(Comparator.comparingLong(Message::getTime))
Added to Comparator in Java 8: static <T extends Comparable<? super T>> Comparator<T> naturalOrder() Use it like this, for example: Comparator<Double> natural = Comparator.<Double>naturalOrder(); return natural.compare(1.0, 1.1));