This week at work a colleague showed a nice feature of the Pattern class in Java: we can easily turn a Pattern into a Predicate with the asPredicate and asMatchPredicate methods. The asPredicate method return a predicate for testing if the pattern can be found given string. And the asMatchPredicate return a predicate for testing if the pattern matches a given string.
In the following example code we use both methods to create predicates:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | package mrhaki;import java.util.List;import java.util.regex.Pattern;import java.util.stream.Collectors;import java.util.stream.Stream;public class PatternPredicate { public static void main(String[] args) { // Sample pattern. var pattern = Pattern.compile("J"); // asPredicate returns a predicate to test if // the pattern can be found in the given string. assert pattern.asPredicate().test("Java"); assert !pattern.asPredicate().test("Groovy"); // asMatchPredicate returns a predicate to test if // the pattern completely matches the given string. assert pattern.asMatchPredicate().test("J"); assert !pattern.asMatchPredicate().test("Java"); // Using the asPredicate and asMatchPredicate is very // useful with the streams API. var languagesWithJ = Stream.of("Java", "Groovy", "Clojure", "JRuby", "JPython") .filter(pattern.asPredicate()) .collect(Collectors.toList()); assert languagesWithJ.size() == 3; assert languagesWithJ.equals(List.of("Java", "JRuby", "JPython")); var startsWith_J_EndsWith_y = Pattern.compile("^J\\w+y$").asMatchPredicate(); var languagesWithJy = Stream.of("Java", "Groovy", "Clojure", "JRuby", "JPython") .filter(startsWith_J_EndsWith_y) .collect(Collectors.toList()); assert languagesWithJy.size() == 1; assert languagesWithJy.equals(List.of("JRuby")); }} |
Written with Java 13.
