Tutorial by Examples: e

// Java: Map<Boolean, List<Student>> passingFailing = students.stream() .collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD)); // Kotlin: val passingFailing = students.partition { it.grade >= PASS_THRESHOLD }

// Java: List<String> namesOfMaleMembersCollect = roster .stream() .filter(p -> p.getGender() == Person.Sex.MALE) .map(p -> p.getName()) .collect(Collectors.toList()); // Kotlin: val namesOfMaleMembers = roster.filter { it.gender == Person.Sex.MALE }.map { it.nam...

// Java: Map<Person.Sex, List<String>> namesByGender = roster.stream().collect( Collectors.groupingBy( Person::getGender, Collectors.mapping( Person::getName, Collectors.toList()))); // ...

// Java: List<String> filtered = items.stream() .filter( item -> item.startsWith("o") ) .collect(Collectors.toList()); // Kotlin: val filtered = items.filter { item.startsWith('o') }

// Java: String shortest = items.stream() .min(Comparator.comparing(item -> item.length())) .get(); // Kotlin: val shortest = items.minBy { it.length }

// Java: Stream.of("a1", "a2", "a3") .findFirst() .ifPresent(System.out::println); // Kotlin: sequenceOf("a1", "a2", "a3").firstOrNull()?.apply(::println)

// Java: IntStream.range(1, 4).forEach(System.out::println); // Kotlin: (inclusive range) (1..3).forEach(::println)

// Java: Arrays.stream(new int[] {1, 2, 3}) .map(n -> 2 * n + 1) .average() .ifPresent(System.out::println); // 5.0 // Kotlin: arrayOf(1,2,3).map { 2 * it + 1}.average().apply(::println)

// Java: Stream.of("a1", "a2", "a3") .map(s -> s.substring(1)) .mapToInt(Integer::parseInt) .max() .ifPresent(System.out::println); // 3 // Kotlin: sequenceOf("a1", "a2", "a3") .map { it.substring(1) } ...

// Java: IntStream.range(1, 4) .mapToObj(i -> "a" + i) .forEach(System.out::println); // a1 // a2 // a3 // Kotlin: (inclusive range) (1..3).map { "a$it" }.forEach(::println)

// Java: Stream.of(1.0, 2.0, 3.0) .mapToInt(Double::intValue) .mapToObj(i -> "a" + i) .forEach(System.out::println); // a1 // a2 // a3 // Kotlin: sequenceOf(1.0, 2.0, 3.0).map(Double::toInt).map { "a$it" }.forEach(::println)

// Java: long count = items.stream().filter( item -> item.startsWith("t")).count(); // Kotlin: val count = items.filter { it.startsWith('t') }.size // but better to not filter, but count with a predicate val count = items.count { it.startsWith('t') }

// Java: List<String> myList = Arrays.asList("a1", "a2", "b1", "c2", "c1"); myList.stream() .filter(s -> s.startsWith("c")) .map(String::toUpperCase) .sorted() .forEach(System.out::println); // C1 ...

// Java: Arrays.asList("a1", "a2", "a3") .stream() .findFirst() .ifPresent(System.out::println); // Kotlin: listOf("a1", "a2", "a3").firstOrNull()?.apply(::println) or, create an extension function on String calle...

// Java: String phrase = persons .stream() .filter(p -> p.age >= 18) .map(p -> p.name) .collect(Collectors.joining(" and ", "In Germany ", " are of legal age.")); System.out.println(phrase); // In Germany Max and Peter a...

// Java: Map<Integer, String> map = persons .stream() .collect(Collectors.toMap( p -> p.age, p -> p.name, (name1, name2) -> name1 + ";" + name2)); System.out.println(map); // {18=Max, 23=Peter;Pamela, ...

// Java (verbose): Collector<Person, StringJoiner, String> personNameCollector = Collector.of( () -> new StringJoiner(" | "), // supplier (j, p) -> j.add(p.name.toUpperCase()), // accumulator (j1, j2) -> j1.merge(j2), // c...

// Java: IntSummaryStatistics ageSummary = persons.stream() .collect(Collectors.summarizingInt(p -> p.age)); System.out.println(ageSummary); // IntSummaryStatistics{count=4, sum=76, min=12, average=19.000000, max=23} // Kotlin: // something to hold the stats... da...

CRTP is a powerful, static alternative to virtual functions and traditional inheritance that can be used to give types properties at compile time. It works by having a base class template which takes, as one of its template parameters, the derived class. This permits it to legally perform a static_c...

Subroutines are created by using the keyword sub followed by an identifier and a code block enclosed in braces. You can access the arguments by using the special variable @_, which contains all arguments as an array. sub function_name { my ($arg1, $arg2, @more_args) = @_; # ... } Sin...