Java Developer

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Java 9 New Features

11 Jan 2018

Java history

JDK 1.6 Mustang 2006

  • Scripting Language Support
  • JDBC 4.0 Support
  • Java Compiler API
  • Pluggagble Annotations
  • Native PKI, Java GSS, Kerberos and LDAP support
  • Integerated Web Services
  • Light weight

JDK 1.7 Dolphin 2011

  • JVM support for dynamic languages
  • Compressed 64-bit pointers
  • Strings in switch
  • Automatic resource management in try-statement
  • The diamond operator
  • Simplified varargs method declaration
  • Binary integer literals
  • Improved exception handling
  • ForkJoin Framework
  • G1 Garbage Collector

JDK 1.8 Spider 2014

  • Lambda expression support in APIs
  • Functional interface and default methods
  • Optionals
  • Annotation on Java Types
  • Unsigned Integer Arithmetic
  • Repeating annotations
  • New Date and Time API
  • Statically-linked JNI libraries
  • Launch JavaFX applications from jar files
  • Remove the permanent generation from GC

JDK 1.9 Jigsaw 2017

  • JShell : the interactive Java REPL (Read Evaluate Print Loop)
  • Factory Methods for Immutable List, Set, Map and Map.Entry
  • Private methods in interface
  • Try with Resources Improvement
  • CompletableFuture API Improvement
  • Reactive Streams
  • Support for multi-gigabyte heaps
  • Better native code integration
  • Self-tuning JVM
  • Java Module System
  • Money and Currency API
  • Automatic parallelization

Java 9

JShell

G:\>jshell
|  Welcome to JShell -- Version 9-ea
|  For an introduction type: /help intro


jshell> int a = 10
a ==> 10

jshell> System.out.println("a value = " + a )
a value = 10

Factory Methods for Immutable List, Set, Map

//Case List
List immutableList = List.of(); -> Empty List
List immutableList = List.of("one", "two", "three"); -> Non Empty

//Case Map
Map immutableMap = Map.of(); -> Empty Map
Map immutableMap = Map.of(1, "one", 2, "two", 3, "three");

Private methods in Interfaces

//Case JDK 1.8
public interface DBLogging{
      // default method example
      default void logWarn(String message){
         // Step 1: Connect to DataStore
         // Step 2: Log Warn Message
         // Step 3: Close the DataStore connection
      }
      default void logError(String message){
         // Step 1: Connect to DataStore
         // Step 2: Log Error Message
         // Step 3: Close the DataStore connection
      }
}

//Case JDK 1.9
public interface DBLogging {
  // abstract method example
  void logInfo(String message);

  default void logWarn(String message) {
    log(message, "WARN");
  }

  default void logError(String message) {
    log(message, "ERROR");
  }

  default void logFatal(String message) {
    log(message, "FATAL");
  }

  private void log(String message, String msgPrefix) {
	// Step 1: Connect to DataStore
	// Step 2: Log Message with Prefix and styles etc.
	// Step 3: Close the DataStore connection
  }
}

Process API improvements

Process API를 위해 2개의 인터페이스가 추가되었습니다.

java.lang.ProcessHandle
java.lang.ProcessHandle.Info

ProcessHandle currentProcess = ProcessHandle.current();
System.out.println(currentProcess.getPid());

Try With Resources Improvement

Try-with-Resources는 JDK 1.7에 이미 추가가 되었습니다. 기존대비, 조금 더 읽기 쉽고, 널체크를 하지 않아도 되도록 개선이 되었습니다.

//Case JDK 1.7
void testARM_Before_Java9() throws IOException{
 BufferedReader reader1 = new BufferedReader(new FileReader("journaldev.txt"));
 try (BufferedReader reader2 = reader1) {
   System.out.println(reader2.readLine());
 }
}

//Case JDK 1.9
void testARM_Java9() throws IOException{
 BufferedReader reader1 = new BufferedReader(new FileReader("journaldev.txt"));
 try (reader1) {
   System.out.println(reader1.readLine());
 }
}

JDK 1.9 이전에는 try에 reader1을 바로 쓰지 못하고, read2로 복사를 해야했습니다. try에 있는 Closeable 개체는 close를 호출하지 않아도 됩니다.

CompletableFuture API Improvement

Delay

//Delay
future.completeAsync(supplier, CompletableFuture.delayedExecutor(3, TimeUnit.SECONDS))
      .thenAccept(result -> System.out.println("accept: " + result));

orTimeout

// TIMEOUT = 3;
// doWork() takes 5 seconds to finish

CompletableFuture<String> future =
	doWork("JavaSampleApproach")
	.orTimeout(TIMEOUT, TimeUnit.SECONDS)
	.whenComplete((result, error) -> {
		if (error == null) {
			System.out.println("The result is: " + result);
		} else {
			System.out.println("Sorry, timeout in " + TIMEOUT + " seconds");
		}
	});

completeOnTimeout

// TIMEOUT = 3;
// doWork() takes 5 seconds to finish

CompletableFuture<String> future =
  doWork("JavaSampleApproach")
  .completeOnTimeout("JavaTechnology", TIMEOUT, TimeUnit.SECONDS)
  .whenComplete((result, error) -> {
    if (error == null) {
	  System.out.println("Case 1");
	} else {
	  System.out.println("Case 2");
	}
  });

결과는 The result is: Case 1 입니다.

Reactive Streams

자바 언어를 이용해서 매우 쉽게 병행성, 확장성, 비동기 애플리케이션을 구현한 Publish / Subscribe 프레임워크가 추가되었습니다.

  • java.util.concurrent.Flow
  • java.util.concurrent.Flow.Publisher
  • java.util.concurrent.Flow.Subscriber
  • java.util.concurrent.Flow.Processor

Stream API Improvements

  • dropWhile
  • takeWhile
Stream.of("a", "b", "c", "", "e")
	.takeWhile(s -> !String.isEmpty(s));
	.forEach(System.out::print);

결과는 Console: abc 입니다.

Module System

Java SE9 버전 전에는 모노리틱 jar방식에서 탈피할수 있게 되었습니다. 개인적으로 java9에서 가장 기대가 되는 기능입니다.

  • 참조하는 다른 모듈을 명시
  • 외부로 노출하는 패키지 명시

참조

  • https://infoscis.github.io/2017/03/24/First-steps-with-java9-and-jigsaw-part-1/