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); } }