jshell> int i = 128
i ==> 128

jshell> i instanceof byte
$2 ==> false

jshell> i = 127
i ==> 127

jshell> i instanceof byte
$4 ==> true

jshell> double d = 1
d ==> 1.0

jshell> d instanceof int
$2 ==> true

jshell> d = 1.2
d ==> 1.2

jshell> d instanceof int
$4 ==> false

jshell> Long num = 123L
num ==> 123

jshell> num instanceof int
|  エラー:
|  不適合な型: java.lang.Longをintに変換できません:
|  num instanceof int
|  ^-^

jshell> num instanceof long
$7 ==> true

jshell> long num = 123
num ==> 123

jshell> var out = new ByteArrayOutputStream()
out ==>

jshell> if (num instanceof byte b) out.write(b)

jshell> out.toByteArray()
$21 ==> byte[1] { 123 }

jshell> num = 1234
num ==> 1234

jshell> if (num instanceof byte b) out.write(b)

jshell> out.toByteArray()
$24 ==> byte[1] { 123 }

jshell> long num = 1234
num ==> 1234

jshell> switch (num) { case int n -> "いんと"; default -> "それ以外";}
$25 ==> "いんと"

jshell> num = 30_0000_0000L
num ==> 3000000000

jshell> switch (num) { case int n -> "いんと"; default -> "それ以外";}
$27 ==> "それ以外"

boolean flag = isFoo();
var s = switch (flag) {
  case true -> "たった";
  case false -> "おりた";
}

import module java.base;

>jshell
|  JShellへようこそ -- バージョン23
|  概要については、次を入力してください: /help intro

jshell> LocalDate.now()
|  エラー:
|  シンボルを見つけられません
|    シンボル:   変数 LocalDate
|    場所: クラス
|  LocalDate.now()
|  ^-------^

>jshell --enable-preview
|  JShellへようこそ -- バージョン23
|  概要については、次を入力してください: /help intro

jshell> LocalDate.now()
$1 ==> 2024-10-11

jshell> import module java.desktop;

jshell> var f = new JFrame("hello")
f ==> javax.swing.JFrame[frame0,0,0,0x0,invalid,hidden, ... tPaneCheckingEnabled=true]

jshell> var b = new JButton("OK")
b ==> javax.swing.JButton[,0,0,0x0,invalid,alignmentX=0 ... xt=OK,defaultCapable=true]

jshell> List a = null;
|  エラー:
|  Listの参照はあいまいです
|    java.awtのクラス java.awt.Listとjava.utilのインタフェース java.util.Listの両方が一致します
|  List a = null;
|  ^--^

jshell> import java.util.List

jshell> List a = null
a ==> null

public class Hello {
  public static void main(String[] args) {
    System.out.println("Hello Java!");
  }
}

void main() {
  println("Hello Java!");
}

>more Hello.java
void main() {
  println("Hello Java!");
}

>java --enable-preview --source 23 Hello.java
ノート: Hello.javaはJava SE 23のプレビュー機能を使用します。
ノート: 詳細は、-Xlint:previewオプションを指定して再コンパイルしてください。
Hello Java!

public class Hello {
  public void main(String[] args) {
    foo();
  }
  void foo() {
    System.out.println("Hello");
  }
}

new Object() {
  void main() {
    println("Hello Java");
  }
}.main();

>java --enable-preview --source 23 static.java
static.java:3: エラー: 不正なファイル名: static
  void main() {
  ^
エラー1個
エラー: コンパイルが失敗しました

import static java.io.IO.*;

public class Hello {
  public void main(String[] args) {
    foo();
  }
  void foo() {
    println("Hello");
  }
}

void main() {
 var data = List.of("test", "data");
 println(data.stream().collect(Collectors.joining(" ")));
}

class Foo {
  Foo(List l1, List l2) {
  }
}

class Bar extends Foo {
  Bar() {
    super(List.of("abc", "def"), List.of("abc", "def"));
  }
}

class Bar extends Foo {
  private Bar(List l) {
    super(l, l);
  }
  Bar() {
    this(List.of("abc", "def"));
  }
}

class Bar extends Foo {
  Bar() {
    var param = List.of("abc", "def");
    super(param, param);
  }

class Bar extends Foo {
  List<String> param;
  Bar() {
    param = List.of("abc", "def");
    super(param, param);
  }
}

test.java:11: エラー: スーパータイプのコンストラクタの呼出し前はparamを参照できません
    param = List.of("abc", "def");
    ^

jshell> var f = NumberFormat.getInstance()
f ==> DecimalFormat [locale: "日本語 (日本)", pattern: "#,##0.###"]

jshell> f.isStrict()
$9 ==> false

jshell> f.parse("1,234円")
$10 ==> 1234

jshell> f.setStrict(true)

jshell> f.parse("1,234円")
|  例外java.text.ParseException: Unparseable number: "1,234円"
|        at NumberFormat.parse (NumberFormat.java:464)
|        at (#12:1)

jshell> var i = Instant.now()
i ==> 2024-10-08T21:08:15.820407600Z

jshell> i.until(Instant.now())
$19 ==> PT24.3460241S

jshell> i.until(Instant.now())
$20 ==> PT30.088317S

import jdk.incubator.vector.*;
static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_256;

void vectorComputation(float[] a, float[] b, float[] c) {

    for (int i = 0; i < a.length; i += SPECIES.length()) { // SPECIES.length() = 256bit / 32bit -> 8
        VectorMask<Float> m = SPECIES.indexInRange(i, a.length); // 端数がマスクされる
                                                                 // a.lengthが11でiが8のとき最初の3つしか要素がないので [TTT.....]
		// FloatVector va, vb, vc;
        FloatVector va = FloatVector.fromArray(SPECIES, a, i, m);
        FloatVector vb = FloatVector.fromArray(SPECIES, b, i, m);
        FloatVector vc = va.mul(va).
                    add(vb.mul(vb)).
                    neg();
        vc.intoArray(c, i, m);
    }
}

jshell> FloatVector.SP
SPECIES_128         SPECIES_256         SPECIES_512      
SPECIES_64          SPECIES_MAX         SPECIES_PREFERRED   

jshell> FloatVector.SPECIES_PREFERRED
$11 ==> Species[float, 8, S_256_BIT]

jshell> va.
abs()                    add(                     addIndex(
bitSize()                blend(                   broadcast(
byteSize()               castShape(               check(
compare(                 compress(                convert(
convertShape(            div(                     elementSize()
elementType()            eq(                      equals(
expand(                  fma(                     getClass()
hashCode()               intoArray(               intoMemorySegment(
lane(                    lanewise(                length()
lt(                      maskAll(                 max(
min(                     mul(                     neg()
notify()                 notifyAll()              pow(
rearrange(               reduceLanes(             reduceLanesToLong(
reinterpretAsBytes()     reinterpretAsDoubles()   reinterpretAsFloats()
reinterpretAsInts()      reinterpretAsLongs()     reinterpretAsShorts()
reinterpretShape(        selectFrom(              shape()
slice(                   species()                sqrt()
sub(                     test(                    toArray()
toDoubleArray()          toIntArray()             toLongArray()
toShuffle()              toString()               unslice(
viewAsFloatingLanes()    viewAsIntegralLanes()    wait(
withLane(  

jshell> IntStream.range(0, 10).boxed()
                 .gather(Gatherers.windowFixed(3))
                 .toList()
$1 ==> [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]]

jshell> IntStream.range(0, 10).boxed()
                 .gather(Gatherers.windowSliding(3))
                 .toList()
$2 ==> [[0, 1, 2], [1, 2, 3], [2, 3, 4], [3, 4, 5],
        [4, 5, 6], [5, 6, 7], [6, 7, 8], [7, 8, 9]]

jshell> IntStream.range(0, 10).boxed()
                 .gather(Gatherers.mapConcurrent(4, n -> n * 2))
                 .toList()
$3 ==> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

jshell> IntStream.range(0, 10).boxed()
                 .map(n -> n * 2)
                 .toList()
$4 ==> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

jshell> IntStream.range(0, 10).boxed()
                 .gather(Gatherers.scan(() -> "*", (s, n) -> s + n))
                 .toList()
$7 ==> [*0, *01, *012, *0123, *01234, *012345,
        *0123456, *01234567, *012345678, *0123456789]

jshell> IntStream.range(0, 10).boxed()
                 .gather(Gatherers.fold(() -> "*", (s, n) -> s + n))
                 .toList()
$8 ==> [*0123456789]

jshell> IntStream.range(0, 10).boxed().reduce(0, (a, b) -> a + b)
$9 ==> 45

jshell> IntStream.range(0, 10).parallel().boxed()
                 .collect(Collectors.reducing(
                         "*", n -> "" + n, (s, t) -> s + t))
$12 ==> "*0*1*2*3*4*5*6*7*8*9"

jshell> IntStream.range(0, 10).parallel().boxed().gather(Gatherers.fold(() -> "*", (s, n) -> s + n)).findAny().get()
$14 ==> "*0123456789"

Response handle() throws ExecutionException, InterruptedException {
    try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
        Subtask<String>  user  = scope.fork(() -> findUser());
        Subtask<Integer> order = scope.fork(() -> fetchOrder());

        scope.join()            // Join both forks
             .throwIfFailed();  // ... and propagate errors

        // Here, both forks have succeeded, so compose their results
        return new Response(user.get(), order.get());
    }
}

void start() {
  proc1("test");
}

void proc1(String str) {
  System.out.println(str);
  proc2(str);
}

void proc2(String str) {
  System.out.println(str);
}

String str;

void start() {
  str = "test";
  proc1();
}

void proc1() {
  System.out.println(str);
  proc2();
}

void proc2() {
  System.out.println(str);
}

final ThreadLocal<String> VAR = new ThreadLocal<>();

void start() {
  VAR.set("test");
  proc1();
}

void proc1() {
  System.out.println(VAR.get());
  proc2();
}

void proc2() {
  System.out.println(VAR.get());
}

final ScopedValue<String> VAR = new ScopedValue<>();

void start() {
  ScopedValue.where(VAR, "test")
    .run(() -> proc1());
}

void proc1() {
  System.out.println(VAR.get());
  proc2();
}

void proc2() {
  System.out.println(VAR.get());
}