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Modern Java Features
- 1. 1 / 22 ModernJava Features for Better Code Florian Hopf, Zenika
- 2. 2 / 22 Agenda ●Try with Resources ● Optional ● Date and Time API ● Lambda Expressions ● Streams
- 3. 3 / 22 Trywith Resources ● Aka Automatic resource management ● Helps with forgetting closing resources – Files – IO Streams – Database connections – ...
- 4. 4 / 22 TraditionalApproach FileInputStream in = null; try { in = new FileInputStream("some-file.txt"); // do something with in } catch (IOException ex) { // log or throw exception } finally { if (in != null) { try { in.close(); } catch (IOException ex) { // do nothing }
- 5. 5 / 22 Trywith Resources try (FileInputStream in = new FileInputStream("some-file.txt")) { // do something with in } catch(IOException ex) { // log or throw exception }
- 6. 6 / 22 Trywith Resources ● Will work everywhere you would expect it ● Use it whenever you need to close something ● Interface AutoClosable as a marker
- 7. 7 / 22 Optional ●Can replace working with null values ● Can prevent NullPointerExceptions
- 8. 8 / 22 Classicnull check public void classicNull() { String result = methodThatCanReturnNull(); if (result != null) { System.out.println(result); } else { System.out.println("Missing value"); } } private String methodThatCanReturnNull() { if (something) { return "Hello"; }
- 9. 9 / 22 Optional publicvoid optional() { Optional<String> result=methodWithOptional(); System.out.println( result.orElse("Missing value")); } private Optional<String> methodWithOptional() { if (something) { return Optional.of("Hello"); } return Optional.empty(); }
- 10. 10 / 22 OptionalCommon Methods ● Creating – of, ofNullable, empty ● Checking – isPresent ● Retrieving – get, orElse, map, filter, ...
- 11. 11 / 22 Optional ●Can be useful as return value from methods ● Semantic meaning: Value can be absent, needs check ● Null has been called “billion dollar mistake” by its inventor
- 12. 12 / 22 Dateand Time API ● Replacement for java.util.Date and Calendar ● Immutable data structures ● Easy manipulation (e.g. date.plusDays(2)) ● Instant: Timestamp ● LocalDate(Time): Date and Time without Timezone ● ZonedDate(Time): Date and Time with Timezones
- 13. 13 / 22 Lambdas ●New syntax to pass functionality to methods ● Can be used to replace single method interfaces () -> System.out.println("Hello"); (String name) -> System.out.println(name); Arrays.sort(strArray, (String s1, String s2) -> s2.length() - s1.length());
- 14. 14 / 22 Lambdas ●Method references can be used as lambdas – Special syntax using :: String::trim ● New interfaces for common functionality – Function, Predicate, Supplier, Consumer
- 15. 15 / 22 Streams ●Functional modification of stream of elements ● map, filter, reduce ● Not related to Java IO-Streams ● Created easily for Collections (List, Set, Map), arrays, File contents, Ranges, ...
- 16. 16 / 22 Classicapproach List<String> fullnameOfMinors = new ArrayList<>(); for (Person person: persons) { if (person.age < 18) { fullnameOfMinors.add(person.name); } }
- 17. 17 / 22 Streams List<String>fullnameOfMinors = persons.stream() .filter(person -> person.age < 18) .map(person -> person.name) .collect(Collectors.toList());
- 18. 18 / 22 Streams ●Intermediate operations – map, filter, distinct, limit, sorted, ... ● Terminal operations – collect, forEach, max, min, ...
- 19. 19 / 22 Streams ●Grouping Map<Integer, List<Person>> personsByAge = persons.stream() .collect(groupingBy(Person::getAge));
- 20. 20 / 22 Streams ●Sorting by comparator List<Person> personsSortedByAge = persons.stream() .sorted( Comparator.comparing(Person::getAge)) .collect(toList());
- 21. 21 / 22 Streams ●Building a String list of elements String stringListOfPersons = persons.stream() .map(person -> person.name) .collect(joining(","));
- 22. 22 / 22 Resources ●https://leanpub.com/whatsnewinjava8/read ● https://zeroturnaround.com/rebellabs/java-8-streams-che