Java14的新特性

java -version
openjdk version "14" 2020-03-17
OpenJDK Runtime Environment (build 14+36-1461)
OpenJDK 64-Bit Server VM (build 14+36-1461, mixed mode, sharing)

    public boolean isBadRequestError(Exception ex) {
        return (ex instanceof HttpClientErrorException rce) &&
                HttpStatus.BAD_REQUEST == rce.getStatusCode();
    }

jpackage --name myapp --input lib --main-jar main.jar

public class AgentMain implements Runnable {

    public static void premain(String agentArgs, Instrumentation inst) {
        try {
            Logger.getLogger("AgentMain").log(
                    Level.INFO, "Attaching JFR Monitor");
            new Thread(new AgentMain()).start();
        } catch (Throwable t) {
            Logger.getLogger("AgentMain").log(
                    Level.SEVERE,"Unable to attach JFR Monitor", t);
        }
    }

    @Override
    public void run() {
        var sender = new JfrStreamEventSender();
        try (var rs = new RecordingStream()) {
            rs.enable("jdk.CPULoad")
                    .withPeriod(Duration.ofSeconds(1));
            rs.enable("jdk.JavaMonitorEnter")
                    .withThreshold(Duration.ofMillis(10));
            rs.onEvent("jdk.CPULoad", sender);
            rs.onEvent("jdk.JavaMonitorEnter", sender);
            rs.start();
        }
    }
}

public class NullPointerExample {

    public record City(String name){

    }

    public record Location(City city) {

    }

    public record User(String name, Location location) {

    }

    public static void main(String[] args){
        User user = new User("hello", new Location(null));
        System.out.println(user.location().city().name());
    }
}

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "com.example.NullPointerExample$City.name()" because the return value of "com.example.NullPointerExample$Location.city()" is null
    at com.example.NullPointerExample.main(NullPointerExample.java:25)

public record Point(int x, int y) {

    public Point {
        System.out.println(String.format("(%d,%d)", x, y));
    }

    public Point(int value) {
        this(value, value);
    }

    public static Point of(int value) {
        return new Point(value, value);
    }
}

javac --enable-preview -source 14 Point.java
javap -verbose Point.class
Compiled from "Point.java"
public final class com.example.domain.Point extends java.lang.Record {
  public com.example.domain.Point(int, int);
  public static com.example.domain.Point of(int);
  public java.lang.String toString();
  public final int hashCode();
  public final boolean equals(java.lang.Object);
  public int x();
  public int y();
}

    public void testSwitchWithArrowBlockAndYield() {
        int n = 3;
        String quantityString = switch (n) {
            case 1 -> "one";
            case 2 -> "two";
            default -> {
                System.out.println("default");
                yield "many";
            }
        };
        System.out.println(quantityString);
    }

OpenJDK 64-Bit Server VM warning: Ignoring option UseConcMarkSweepGC; support was removed in 14.0

-XX:+UnlockExperimentalVMOptions -XX:+UseZGC

-XX:+UnlockExperimentalVMOptions -XX:+UseZGC

OpenJDK 64-Bit Server VM warning: Option UseParallelOldGC was deprecated in version 14.0 and will likely be removed in a future release.

    @Test
    public void testTextBlockWithTwoNewEscapeSequences() {
        String inOneLine = """
                Lorem ipsum dolor sit amet, consectetur adipiscing \
                elit, sed do eiusmod tempor incididunt ut labore \
                et dolore magna aliqua.\
                """;
        System.out.println(inOneLine);

        String singleSpace = """
                red  \s
                green\s
                blue \s
                """;
        System.out.println(singleSpace);
    }

    @Test
    public void testForeignMemoryAccessAPI() {
        SequenceLayout intArrayLayout
                = MemoryLayout.ofSequence(25,
                MemoryLayout.ofValueBits(32,
                        ByteOrder.nativeOrder()));

        VarHandle intElemHandle
                = intArrayLayout.varHandle(int.class,
                MemoryLayout.PathElement.sequenceElement());

        try (MemorySegment segment = MemorySegment.allocateNative(intArrayLayout)) {
            MemoryAddress base = segment.baseAddress();
            for (int i = 0; i < intArrayLayout.elementCount().getAsLong(); i++) {
                intElemHandle.set(base, (long) i, i);
            }
        }
    }

    default void declaration(String version, String encoding, String standalone)
        throws SAXException
    {
        //no op
    }

Thread.suspend()
Thread.resume()
ThreadGroup.suspend()
ThreadGroup.resume()
ThreadGroup.allowThreadSuspension(boolean)