Originally forked from https://github.com/zupzup/java8-functional-katas but needed to move to my separate repo since the owner didn't review my PR
Some Katas for functional programming in Java 8 for a coding dojo (loosely based on http://reactive-extensions.github.io/learnrx/ and converted to Java)
Just read the instructions in the Kata and try to finish them. You can also use TDD if you want - there are dummy tests for all Katas.
- Kata 1: simple projection using map
- Kata 2: filter() and map()
- Kata 3: using map() and flattening the array using flatMap()
- Kata 4: a simple query using map(), filter() and flatMap()
- Kata 5: simple example using reduce()
- Kata 6: map() and reduce() combined
- Kata 7: more advanced queryin
- Kata 8: combining collections using zip()
- Kata 9: Complex Query
- Kata 10: Transforming a data structure
- Kata 11: Transforming a more complex data structure
public class Exercise1 {
public static void main(String[] args) {
// Use StreamSources.intNumbersStream() and StreamSources.userStream()
// Print all numbers in the intNumbersStream stream
//TODO: Write code here
StreamSources.intNumbersStream().forEach(System.out::println);
System.out.println("---------------------------------------");
// Print numbers from intNumbersStream that are less than 5
//TODO: Write code here
StreamSources.intNumbersStream().filter(integer -> integer < 5).forEach(System.out::println);
System.out.println("---------------------------------------");
//Print the second and third numbers in intNumbersStream that's greater than 5
//TODO: Write code here
StreamSources.intNumbersStream().filter(integer -> integer > 5)
//we skip the 0 from 0, 2,4
.skip(1)
//and we take last two elements after first element so those will be the second and the third
.limit(2).forEach(System.out::println);
System.out.println("---------------------------------------");
// Print the first number in intNumbersStream that's greater than 5
// If nothing is found, print -1
//TODO: Write code here
Integer result = StreamSources.intNumbersStream()
.filter(integer -> integer > 5)
.findFirst()
.orElse(-1);
System.out.println(result);
System.out.println("---------------------------------------");
// Print firstNames of all users in userStream
//TODO: Write code here
StreamSources.userStream()
.map(user -> user.getName())
.forEach(firstName -> System.out.println(firstName));
System.out.println("---------------------------------------");
//Combining 2 streams
//Print surnames in userStream for all the users those have IDs from the numberSteam
//TODO: Write code here
//Bad way
StreamSources.intNumbersStream()
.flatMap(id -> StreamSources.userStream().filter(user -> user.getId() == id))
.map(user -> user.getSurname())
.forEach(surname -> System.out.println(surname));
System.out.println("---------------------------------------");
//Better way
StreamSources.userStream()
.filter(user -> StreamSources.intNumbersStream().anyMatch(id -> user.getId() == id))
.map(user -> user.getSurname())
.forEach(System.out::println);
}
}
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