Tutorial by Examples: er

Filter a list to another list

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

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #2 - lazily using first item if exists

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

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #3 - iterate a range of Integers

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

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #4 - iterate an array, map the values, calculate the average

// 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)

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #5 - lazily iterate a list of strings, map the values, convert to Int, find max

// 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) } ...

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #6 - lazily iterate a stream of Ints, map the values, print results

// 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)

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #7 - lazily iterate Doubles, map to Int, map to String, print each

// 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)

Kotlin • Java 8 Stream Equivalents

Counting items in a list after filter is applied

// 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') }

Kotlin • Java 8 Stream Equivalents

How streams work - filter, upper case, then sort a list

// 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 ...

Kotlin • Java 8 Stream Equivalents

Different Kinds of Streams #1 - eager using first item if it exists

// 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...

Kotlin • Java 8 Stream Equivalents

Collect example #6 - group people by age, print age and names together

// 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, ...

Kotlin • Java 8 Stream Equivalents

Collect example #7a - Map names, join together with delimiter

// 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...

Kotlin • Java 8 Stream Equivalents

The Curiously Recurring Template Pattern (CRTP)

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...

C++ • Curiously Recurring Template Pattern (CRTP)

External CSS Stylesheet

HTML • Linking Resources

Generating Build Environment with CMake

CMake generates build environments for nearly any compiler or IDE from a single project definition. The following examples will demonstrate how to add a CMake file to the cross-platform "Hello World" C++ code. CMake files are always named "CMakeLists.txt" and should already exis...

C++ • Build Systems

Building an image from a Dockerfile

Once you have a Dockerfile, you can build an image from it using docker build. The basic form of this command is: docker build -t image-name path If your Dockerfile isn't named Dockerfile, you can use the -f flag to give the name of the Dockerfile to build. docker build -t image-name -f Dockerfi...

Docker • Building images

A simple Dockerfile

FROM node:5 The FROM directive specifies an image to start from. Any valid image reference may be used. WORKDIR /usr/src/app The WORKDIR directive sets the current working directory inside the container, equivalent to running cd inside the container. (Note: RUN cd will not change the current ...

Docker • Building images

SSL Certs Expiring

This data is collected by the http_unit and scollector. It warns when an alert is going to expire within a certain amount of days, and then goes critical if the cert has passed the expiration date. This follows the recommended default of warn and crit usage in Bosun (warn: something is going to fail...

Bosun • Complete Examples

Header Template

In Bosun templates can reference other templates. For emails notifications, you might have a header template to show things you want in all alerts. Header Template template header { body = ` <style> td, th { padding-right: 10px; } </style> <p s...

Bosun • Complete Examples

Low Memory Alert and Template

Templates can be previewed and edited using the Rule Editor tab in Bosun. Use the Jump to links to select the alert you want to edit, then you can use the template button next to macro to switch between the alert an template sections of the configuration. If an alert has multiple instances you can u...

Bosun • Templates: Overview