mgrzeszczak / beyond-java-8

Updated list of Java language features beyond Java 8.

Beyond Java 8

This is an updated list of language related (syntax, methods) features that are present if later versions of Java (beyond 8). Each feature will be provided with an example (sometimes pseudo-code like).

Java 9

1. Private interface methods - to have reusable methods to use in default interface methods

   interface TestInterface {
   
       private void log(message) {
           System.out.println(message);
       }
   
       default ... action1() {
           ...
           log(...)
           ...
       }
   
       default ... action2() {
           ...
           log(...)
           ...
       }
   
   }
   

2. Collection static factory methods - it is finally possible to create instances of List, Set and Map using a static constructor with concise syntax

   List.of(1,2,3)
   Set.of(1,2,3)
   Map.of("key1", "value1", "key2", "value2")
   Map.ofEntries(Map.entry("key1", "value2"), Map.entry("key2", "value2"))
   

3. New stream methods

   • Stream.ofNullable - create stream from a possibly null object

   Stream.ofNullable(null) == Stream.empty()
   

   • dropWhile - skip elements as long as predicate is satisfied

   Stream.of(1,2,3)
       .dropWhile(i -> i < 2) == Stream.of(2,3)
   

   • takeWhile - take elements as long as predicate is satisfied and discard the rest

   Stream.of(1,2,3)
       .takeWhile(i -> i < 2) == Stream.of(1)
   

   • iterate - generate a stream as long as predicate is satisfied

   Stream.iterate(0, i -> i < 3; i -> i + 1)
       .collect(Collectors.toList()) == [0,1,2]
   

4. New collector methods

   • Collectors.filtering - filter while collecting

   Stream.of(1,2,3)
       .collect(Collectors.filtering(i -> i < 2), Collectors.toList()) == [1]
   

   • Collectors.flatMapping - flat map objects into collection while collecting

   class Process {
       private ProcessType type;
       private List<ProcessInstance> instances;
   }
   
   List<Process> processes = ...
   
   Map<ProcessType, List<ProcessInstance>> instancesByType = processes.stream()
       .collect(Collectors.groupingBy(Process::getType, Collectors.flatMapping(p -> p.getInstances().stream(), Collectors.toList())));
   

5. Optional

   • or - allows chaining

   Optional.ofNullable(method1())
    .or(this::method2) // method2 is called only if optional is empty
   

   • stream - create a stream from optional, which is either empty or has one element. Useful if we have a stream of optionals.

   Stream<Optional<?>> stream = ...
   stream
    .flatMap(Optional::stream) // now it's a stream of values
    .collect(Collectors.toList())
   

   • ifPresentOrElse - consume value or execute a runnable if not present

   Optional.of(result)
    .ifPresent(r -> System.out.println("the result is: " + r), () -> System.out.println("No result value"))
   

6. New process API

   • ProcessHandle - allows to control native processes

   ProcessHandle.current().pid()
   ProcessHandle.allProcesses()
   ProcessHandle.of(pid)
   

Java 10

1. Optional
   • orElseThrow - non-parameter version, throws NoSuchElementException when empty

   Integer value = Optional.of(1).orElseThrow()
   

2. Local-Variable Type Inference - it's possible to use var keyword instead of specyfing type for local variables

   var result = calculateStats();
   

License

MIT License

Copyright (c) 2018 Maciej Grzeszczak

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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The above copyright notice and this permission notice shall be included in all
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