java-16-feature

***** 已完成 jdk 16 feature [#B] [100%] :task:
CLOSED: [2021-03-31 三 21:28] SCHEDULED: <2021-03-31 三>
:PROPERTIES:
:REF: https://www.youtube.com/watch?v=1hyWJTjxeGM
:END:

  - State "已完成"     from "进行中"     [2021-03-31 三 21:28]
  - State "进行中"     from "未开始"     [2021-03-31 三 20:35]
  1. Record

     # MyRecord
     public record MyRecord(String name, int id) {

        public MyRecord{
         validateMyFields(id, name);
        }
        public MyRecord(String name, int id){
          validateMyFields(id, name);
          this.name = name;
          this.id = id;
        }

        private void validateMyFields(int id, String name){
         // do validate fields
        }
     }

     # Test MyRecord
     new MyRecord("Trisha", 4326493)

  2. Pattern Matching for InstanceOf

      public class PatternMatchingForInstanceOf{
        public void inspectionToConvertInstanceof(Person person){

          if(person instanceof Employee employee){
              if(employee.isBasedInOffice()){
                employee.workFromHome();
              }
          }
        }
      }

  3. New methods on Stream

     var strings = ArrayList<String>();

     # ModernJava
     strings.stream()
            .filter(s -> s.startsWith("S"))
            .sorted()
            .collect(Collectors.toUnmodifiableList());
     # JDK16
     strings.stream()
            .filter(s-> s.startsWith("S"))
            .sorted()
            .toList();

  4. Warning for Value-Based Classes

     # deprecated in java 9, but new for jdk16 marked for removal JEP 390
     var aDouble = new Double(1.0);
     var aDouble = 1.0;

  5. Local Types

     1. local records

        private Set<Person> filterForPeopleWithFiveOrders(List<Person> people){
          record PersonAndOrders(Person person, List<Order> orders){}

          return people.stream()
                       .map(person -> new PersonAndOrders(person, getOrdersFor(person)))
                       .filter(personAndOrders -> personAndOrders.orders().size() == 5)
                       .map(PersonAndOrders::person)
                       .collect(toUnmodifiableSet());

         }
      2. local enums

         private void organisePeople(List<Person> people){
            enum Role{Employee, Customer, Both, None}

            var peopleByRole = new HashMap<Role, List<Perso>>();

            people.stream()
                  .filter(Person::isCustomer)
                  .forEach(person -> peopleByRole.computeIfAbsent(Role.Customer, role -> new ArrayList<>())
                  .add(person));

         }

  6. Static methods/classes on inner classes

     public class StaticOnInnerClasses{
        static class Outer{
           class NonStaticInnerClass{
              void instanceMethod(){
              }

              # jdk16 static methods on inner classes
              static void staticMethod(){
              }

              # jdk16 static classes inside inner classes
              static class StaticInnerClass{
              }
           }
     }

  7. java 16 preview features

     1. Sealed Types

        public sealed class Colour permits Black, Pink{

        }

        public final class Black extends Colour{

        }

        public non-sealed class Pink extends Colour permits Rose, Magenta{
        }

        public final class Rose extends Pink{

        }

        public final class Magenta extends Pink{

        }

  8. Also available in Java 16

     1. Text Blocks (jdk 14, jdk 13)

     2. Switch Expressions (jdk 12, jdk 13)

  9. Java 11 Features

     1. Local Variable Type Inference

        var

     2. Convenience Factory Methods for Collections

        1. List.of()
        2. Set.of()
        3. Map.of()
        4. Map.ofEntries()

     3. New Methods on Optional

        https://javadevcentral.com/optional-new-methods
        1. ifPresentOrElse()
        2. or()
        3. Stream()
        4. orElseThrow()
        5. isEmpty()

  10. Let your tools do the hard work

Entered on [2021-03-31 三 20:32]