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![371:HiddenClasses
Protectdynamicclassesagainstunpredictableaccess
cannotfindbybytecodelinkageand Class::forName ,
Classloader::loadClass
Normalclasses
ClassLoader::defineClass
Hiddenclasses
MethodHandles.Lookup#defineHiddenClass(byte[]
bytes, boolean initialize,
MethodHandles.Lookup.ClassOption... options)
Generatesahiddenclassfromthebyte[]andreturnsa
lookup objectwithreflectiveaccess
This lookup objectistheonlywaytogetthehidden
Classobject
12](https://image.slidesharecdn.com/linemeetup65-200722082643/75/Head-toward-Java-14-and-Java-15-LINE_DM-12-2048.jpg)
![4: String name = person[i][j][k] // <= Nullable * 4
.getPersonalInformation() // <= Nullable
.getName() // <= Nullable
.getFamilyName() // <= Nullable
.toUpperCase(); // <= Nullable
17](https://image.slidesharecdn.com/linemeetup65-200722082643/75/Head-toward-Java-14-and-Java-15-LINE_DM-17-2048.jpg)
![Case:localvariable
3: String[] names = null;
4: names[1].toLowerCase();
$ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray
Exception in thread "main" java.lang.NullPointerException:
Cannot load from object array // When
because "<local1>" is null // What
at LocalStringArray.main(LocalStringArray.java:4)
$ javac -g LocalStringArray.java // Add all debugging information
$ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray
Exception in thread "main" java.lang.NullPointerException:
Cannot load from object array // When
because "names" is null // What
at LocalStringArray.main(LocalStringArray.java:4)
19](https://image.slidesharecdn.com/linemeetup65-200722082643/75/Head-toward-Java-14-and-Java-15-LINE_DM-19-2048.jpg)
![Openstreamwithrepositorypath
import java.io.IOException;
import java.nio.file.Path;
import jdk.jfr.consumer.EventStream;
public class JFRRemoteSample {
public static void main(String... args) throws IOException {
// Pass repository path via argument
try (EventStream es = EventStream
.openRepository(Path.of(args[0]))) {
// Method Profiling Sample event
es.onEvent("jdk.ExecutionSample", System.out::println);
es.start();
}
}
}
$ java JFRRemoteSample /private/(snip)/2020_05_14_18_57_15_15902
jdk.ExecutionSample {
startTime = 19:09:55.345
sampledThread = "JFR Periodic Tasks" (javaThreadId = 13)
state = "STATE_RUNNABLE"
stackTrace = [
jdk.jfr.internal.PlatformRecorder.periodicTask() line: 474
jdk.jfr.internal.PlatformRecorder.lambda$startDiskMonitor$1() line:
jdk.jfr.internal.PlatformRecorder$$Lambda$52.1546693040.run()
java.lang.Thread.run() line: 832
]
}
35](https://image.slidesharecdn.com/linemeetup65-200722082643/75/Head-toward-Java-14-and-Java-15-LINE_DM-35-2048.jpg)
Uploaded byYuji Kubota
Head toward Java 14 and Java 15 #LINE_DM
Java 14 and 15 introduced several new features and changes including records, pattern matching, text blocks, and updates to the garbage collector. Some notable changes were the addition of records as a new data type, enabling pattern matching for instanceof, and deprecating biased locking and the CMS garbage collector. Tools were also improved with the packaging tool to create installers and event streaming to collect JVM events.
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Head toward Java 14 and Java 15 #LINE_DM
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- 4. Disclaimer I'vetestedthecontentsofthisdocumentbyJDK14.0.2andJDK15 (build32)whichareavailableon jdk.java.net asmuchaspossible, butnotallofthemhavebeentested,sopleasedoanoperation confirmationbeforeyouattempttomodifyyourcode. IconfirmedtheJDKimplementationbyhg.openjdk.java.net/jdk- updates/jdk14u and jdk/jdk . 4
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- 7. 305:PatternMatchingforinstanceof(Preview) Before if (obj instanceofDouble) { Double d = (Double) obj; // Processing with d } After if (obj instanceof Double d) { // Processing with d } thesamewayon switch (Undetermineddate) switch (obj) { case Integer i: // want to do when Integer case Double d: // want to do when Double } NofurtherchangeinJava15(SecondPreview). 7
- 8. 359:Records(Preview) Newtypetocarryadata(like@Value(Lombok)) public record TestRecord(Strings, int i) {} public record TestRecord(String s, int i) { private final String s; private final int i; String s() { return s; } int i() {return i;} TestRecord(String s, int i) { this.s = s; this.i = i; } // toString(), equals(), hashCode() } 8
- 9. 368:TextBlocks(SecondPreview) AddEscape (linebreak),s (space) var textblock = """ Duke is cute s """; var textblock = "Duke is cute "; NofurtherchangeinJava15(Standard). 9
- 10. 370:Foreign‑MemoryAccessAPI(Incubator) 383:Foreign‑MemoryAccessAPI(SecondIncubator) non‑heap allocateDirect :upto2G( Integer.MAX_VALUE)perobject JavaNativeInterface:managememorybyyourself Unsafe.allocateMemory() :potentialremovewithoutwarning VarHandle intHandle = MemoryHandles.varHandle(int.class, ByteOrder.nativeOrder()); try (MemorySegment segment = MemorySegment.allocateNative(100)) { MemoryAddress base = segment.baseAddress(); for (int i = 0; i < 25; i++) { intHandle.set(base.addOffset(i * 4), i); } } --add-modules jdk.incubator.foreign 10
- 11. 360:SealedClasses(Preview) Newtypetorestrictwhichotherclasses/interfacesmay extend/implementthem public sealed classShape permits com.example.polar.Circle, com.example.quad.Rectangle, com.example.quad.simple.Square {...} 11
- 12. 371:HiddenClasses Protectdynamicclassesagainstunpredictableaccess cannotfindbybytecodelinkageand Class::forName , Classloader::loadClass Normalclasses ClassLoader::defineClass Hiddenclasses MethodHandles.Lookup#defineHiddenClass(byte[] bytes,boolean initialize, MethodHandles.Lookup.ClassOption... options) Generatesahiddenclassfromthebyte[]andreturnsa lookup objectwithreflectiveaccess This lookup objectistheonlywaytogetthehidden Classobject 12
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- 15. 358:HelpfulNullPointerExceptions $ java Sample Exceptionin thread "main" java.lang.NullPointerException at Sample.main(Sample.java:4) 15
- 16. 4: String name= person.getName().toUpperCase(); public class Sample { public static void main(String... args){ Person person = new Person(); String name = person.getName().toUpperCase(); } static class Person { String name = null; Person() { } String getName() { return name; } } } 16
- 17. 4: String name= person[i][j][k] // <= Nullable * 4 .getPersonalInformation() // <= Nullable .getName() // <= Nullable .getFamilyName() // <= Nullable .toUpperCase(); // <= Nullable 17
- 18. -XX:+ShowCodeDetailsInExceptionMessages Exception in thread"main" java.lang.NullPointerException: Cannot invoke "String.toUpperCase()" // When because the return value of "Sample$Person.getName()" is null // What $ java -XX:+ShowCodeDetailsInExceptionMessages Sample Exception in thread "main" java.lang.NullPointerException: Cann at Sample.main(Sample.java:4) 18
- 19. Case:localvariable 3: String[] names= null; 4: names[1].toLowerCase(); $ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray Exception in thread "main" java.lang.NullPointerException: Cannot load from object array // When because "<local1>" is null // What at LocalStringArray.main(LocalStringArray.java:4) $ javac -g LocalStringArray.java // Add all debugging information $ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray Exception in thread "main" java.lang.NullPointerException: Cannot load from object array // When because "names" is null // What at LocalStringArray.main(LocalStringArray.java:4) 19
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- 24. 363:RemovetheConcurrentMarkSweep(CMS)Garbage Collector Goodbye -XX:+UseConcMarkSweepGC Ifyousetaboveoption,JVMwilllaunchwithDefaultGC YoushouldspecifyGCalgorthimclearly OpenJDK 64-BitServer VM warning: Ignoring option UseConcMarkSweepGC; support was removed in 14.0 24
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- 29. Basicusage $ jpackage --namesample --input <directory_includes_jar> --main-jar sample.jar --main-class Sample $ ls sample-* sample-1.0.dmg Withcustomruntimeimage: # Show ependent modules $ jdeps -summary Sample.class Sample.class -> java.base Sample.class -> java.desktop # Create runtime image that consists only of dependent modules $ jlink --add-modules java.base,java.desktop --output image # Create installer with custom runtime image $ jpackage --name sample --input <directory_includes_jar> --main-jar sample.jar --main-class Sample --runtime-image image 29
- 30. 349:JFREventStreaming CollecteventsfromlocalJavaprocess import java.time.Duration; import jdk.jfr.consumer.RecordingStream; publicclass JFRSample { public static void main(String... args) { try (RecordingStream rs = new RecordingStream()) { // Enable events JVM will collect periodically rs.enable("jdk.CPULoad") .withPeriod(Duration.ofSeconds(10)); // Registers consumer to perform on event matching a name rs.onEvent("jdk.CPULoad", System.out::println); // Nothing happens when you specify an uncollected event rs.onEvent("jdk.SafepointCleanup", System.out::println); rs.start(); } } } 30
- 31. $ java Sample jdk.CPULoad{ startTime = 18:30:06.225 jvmUser = 1.96% jvmSystem = 0.10% machineTotal = 16.56% } jdk.CPULoad { startTime = 18:30:07.239 jvmUser = 0.26% jvmSystem = 0.03% machineTotal = 16.60% } : 31
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- 33. Useconfigurationinsteadofenablingeventsbyyourself import jdk.jfr.Configuration; import jdk.jfr.consumer.EventStream; importjdk.jfr.consumer.RecordingStream; public class JFRSample { public static void main(String... args) throws Exception { try (RecordingStream rs = new RecordingStream( // Set "default" or "profile" Configuration.getConfiguration("default"))) { // Can register action on events JVM collects by "default" rs.onEvent("jdk.CPULoad", System.out::println); rs.start(); } } } 33
- 34. CollecteventsfromremoteJavaprocessviaRepository -XX:FlightRecorderOptions=repository=/path/to # Launch jshellwith enabling JFR $ jshell -J-XX:StartFlightRecording=maxage=15m,settings=default Started recording 1. : # Check repository path of targeted Java process (jshell) $ jcmd $(pgrep jshell) JFR.configure 14006: Current configuration: Repository path: /private/var/folders/wm/dz3pkjf11hb1mph16365hj1h0000gp/T/2020_ : 34
- 35. Openstreamwithrepositorypath import java.io.IOException; import java.nio.file.Path; importjdk.jfr.consumer.EventStream; public class JFRRemoteSample { public static void main(String... args) throws IOException { // Pass repository path via argument try (EventStream es = EventStream .openRepository(Path.of(args[0]))) { // Method Profiling Sample event es.onEvent("jdk.ExecutionSample", System.out::println); es.start(); } } } $ java JFRRemoteSample /private/(snip)/2020_05_14_18_57_15_15902 jdk.ExecutionSample { startTime = 19:09:55.345 sampledThread = "JFR Periodic Tasks" (javaThreadId = 13) state = "STATE_RUNNABLE" stackTrace = [ jdk.jfr.internal.PlatformRecorder.periodicTask() line: 474 jdk.jfr.internal.PlatformRecorder.lambda$startDiskMonitor$1() line: jdk.jfr.internal.PlatformRecorder$$Lambda$52.1546693040.run() java.lang.Thread.run() line: 832 ] } 35
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