Inside Java Newscast #1 解读（中）

sealed interface Shape permits Rectangle, Circle, Triangle, WeirdShape {}
record Circle(double radius) implements Shape {}
record Rectangle(double width, double height) implements Shape {}
sealed interface Triangle extends Shape permits RightTriangle, NormalTriangle {}
record RightTriangle(double width, double height) implements Triangle {}
record NormalTriangle(double width, double height) implements Triangle {}
static non-sealed class WeirdShape implements Shape {}
class Star extends WeirdShape {}
double area(Shape shape) {
  if (shape instanceof Circle circle)
    return circle.radius() * circle.radius() * Math.PI;
  if (shape instanceof Rectangle rect)
    return rect.width() * rect.height();
  if (shape instanceof RightTriangle rt)
    return rt.width() * rt.height() / 2;
  if (shape instanceof NormalTriangle nt)
    return nt.width() * nt.height() / 2;
  throw new IllegalArgumentException("Unknown shape");
}

double area(Shape shape) {
  return switch (shape) {
    case Circle circle -> circle.radius() * circle.radius() * Math.PI;
    case Rectangle rect -> rect.width() * rect.height();
    case RightTriangle rt -> rt.width() * rt.height() / 2;
    case NormalTriangle nt -> nt.width( ) * nt.height() / 2;
    default -> throw new IllegalArgumentException("Unknown shape");
  };
}

jdeps --jdk-internals -R --class-path 'libs/*' $project

...
JDK Internal API                         Suggested Replacement
----------------                         ---------------------
sun.misc.BASE64Encoder                   Use java.util.Base64 @since 1.8
sun.reflect.Reflection                   Use java.lang.StackWalker @since 9

record Mail(int id, Set<String> sendTo, Set<String> cc) {}

Set<String> collect = mails.stream().flatMap(mail -> {
  Set<String> result = new HashSet<>();
  result.addAll(mail.sendTo());
  result.addAll(mail.cc());
  return result.stream();
}).collect(Collectors.toSet());

Set<String> collect = mails.stream().<String>mapMulti((mail, consumer) -> {
  mail.cc().forEach(consumer::accept);
  mail.sendTo().forEach(consumer::accept);
}).collect(Collectors.toSet());

//创建 UnixDomainSocketAddress
Path socketFile = Path.of("/home/zhanghaxi/process1");
UnixDomainSocketAddress address = UnixDomainSocketAddress.of(socketFile);
//服务端监听
ServerSocketChannel serverChannel = ServerSocketChannel.open(StandardProtocolFamily.UNIX);
serverChannel.bind(address);
SocketChannel channel = serverChannel.accept();
//客户端连接
SocketChannel channel = SocketChannel.open(StandardProtocolFamily.UNIX);
channel.connect(address);

//测试指标为吞吐量
@BenchmarkMode(Mode.Throughput)
//需要预热，排除 jit 即时编译以及 JVM 采集各种指标带来的影响，由于我们单次循环很多次，所以预热一次就行
@Warmup(iterations = 1)
//单线程即可
@Fork(1)
//测试次数，我们测试10次
@Measurement(iterations = 10)
//定义了一个类实例的生命周期，所有测试线程共享一个实例
@State(value = Scope.Benchmark)
public class VectorTest {
  private static final VectorSpecies<Float> SPECIES =
      FloatVector.SPECIES_256;
  final int size = 1000;
  final float[] a = new float[size];
  final float[] b = new float[size];
  final float[] c = new float[size];
  public VectorTest() {
    for (int i = 0; i < size; i++) {
      a[i] = ThreadLocalRandom.current().nextFloat(0.0001f, 100.0f);
      b[i] = ThreadLocalRandom.current().nextFloat(0.0001f, 100.0f);
    }
  }
  @Benchmark
  public void testScalar(Blackhole blackhole) throws Exception {
    for (int i = 0; i < a.length; i++) {
      c[i] = (a[i] * a[i] + b[i] * b[i]) * -1.0f;
    }
  }
  @Benchmark
  public void testVector(Blackhole blackhole) {
    int i = 0;
    //高于数组长度的 SPECIES 一次处理数据长度的倍数
    int upperBound = SPECIES.loopBound(a.length);
    //每次循环处理 SPECIES.length() 这么多的数据
    for (; i < upperBound; i += SPECIES.length()) {
      // FloatVector va, vb, vc;
      var va = FloatVector.fromArray(SPECIES, a, i);
      var vb = FloatVector.fromArray(SPECIES, b, i);
      var vc = va.mul(va)
          .add(vb.mul(vb))
          .neg();
      vc.intoArray(c, i);
    }
    for (; i < a.length; i++) {
      c[i] = (a[i] * a[i] + b[i] * b[i]) * -1.0f;
    }
  }
  public static void main(String[] args) throws RunnerException {
    Options opt = new OptionsBuilder().include(VectorTest.class.getSimpleName()).build();
    new Runner(opt).run();
  }
}