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Java21版本于 2023 年 9 月 19 日发布,自从 Java 改为 6 个月发布一个版本以来,此为如期交付的第 12 个版本。Java21 是 Java 17之后的目前最新的 LTS版本(长期技术支持版本),其中备受关注的新特性是虚拟线程和分带ZGC。虚拟线程在 Java 21中将成为正式功能。Java 21 有望将会成为继 java8 之后又一个流行的 Java 版本。
接下来,让我们一探究竟,和大家分享Java21的新特性。
官方release公告:https://jdk.java.net/21/release-notes
OpenJDK 版本:https://jdk.java.net/21/
Oracle 版本:https://www.oracle.com/java/technologies/downloads/
@Slf4j public class SequencedCollectionDemo { public static void main(String[] args) { // 创建一个Sequenced Collection List<String> sequencedList = new ArrayList<>(); // 添加元素 sequencedList.add("A"); sequencedList.add("B"); sequencedList.add("C"); sequencedList.add("D"); log.info("倒序输出:{}",sequencedList.reversed()); log.info("JAVA8获取首元素:{}",sequencedList.get(0)); log.info("JAVA21获取首元素:{}",sequencedList.getFirst()); log.info("JAVA8获取尾元素:{}",sequencedList.get(sequencedList.size() - 1)); log.info("JAVA21获取尾元素:{}",sequencedList.getLast()); // 删除首个元素 sequencedList.removeFirst(); // 删除末尾元素 sequencedList.removeLast(); log.info("删除首尾元素后:{}",sequencedList); } }
public class RecordTest { record Point(int x, int y) {} record Size(int width, int height) { } record WindowFrame(Point origin, Size size) { } static void printSum(Object obj) { if (obj instanceof Point p) { int x = p.x(); int y = p.y(); System.out.println(x+y); } } static void printSumRecord(Object obj) { if (obj instanceof Point(int x, int y)) { System.out.println(x+y); } } static void printHeight(Object obj) { if (obj instanceof WindowFrame wf) { if (wf.size() != null) { System.out.println("Height: " + wf.size().height()); } } } static void printHeightRecord(Object obj) { if (obj instanceof WindowFrame(Point origin, Size(int width, int height))) { System.out.println("Height: " + height); } } public static void main(String[] args) { printSum(new Point(1, 2)); printSumRecord(new Point(1, 2)); printHeight(new WindowFrame(new Point(1, 2), new Size(3, 4))); printHeightRecord(new WindowFrame(new Point(1, 2), new Size(3, 4))); } }
public class SwitchDemo { public static void main(String[] args) { // 单匹配,不用再写break,支持返回值 System.out.println(swtichTest01()); // 执行多行代码,可使用yield返回 // System.out.println(swtichTest02()); // 多匹配,直接逗号分割 // System.out.println(swtichTest03()); // 匹配增强 // System.out.println(formatter(1)); // System.out.println(formatterPatternSwitch(100L)); // 对于null处理 // testFooBar(null); } public static String swtichTest01() { String day = "MONDAY"; return switch (day) { case "MONDAY" -> "星期1"; case "TUESDAY" -> "星期2"; case "WEDNESDAY" -> "星期3"; case "THURSDAY" -> "星期4"; case "FRIDAY" -> "星期5"; case "SATURDAY" -> "星期6"; case "SUNDAY" -> "星期7"; default -> "未知"; }; } public static String swtichTest02() { String day = "MONDAY"; return switch (day) { case "MONDAY" -> { System.out.println("周一..."); yield "星期1"; } case "TUESDAY" -> "星期2"; case "WEDNESDAY" -> "星期3"; case "THURSDAY" -> "星期4"; case "FRIDAY" -> "星期5"; case "SATURDAY" -> "星期6"; case "SUNDAY" -> "星期7"; default -> "未知"; }; } public static String swtichTest03() { String day = "SATURDAY"; return switch (day) { case "MONDAY" -> { System.out.println("周一..."); yield "星期1"; } case "TUESDAY" -> "星期2"; case "WEDNESDAY" -> "星期3"; case "THURSDAY" -> "星期4"; case "FRIDAY" -> "星期5"; case "SATURDAY","SUNDAY" -> "周末"; default -> "未知"; }; } // java21版本之前 static String formatter(Object obj) { String formatted = "unknown"; if (obj instanceof Integer i) { formatted = String.format("int %d", i); } else if (obj instanceof Long l) { formatted = String.format("long %d", l); } else if (obj instanceof Double d) { formatted = String.format("double %f", d); } else if (obj instanceof String s) { formatted = String.format("String %s", s); } return formatted; } //java21 static String formatterPatternSwitch(Object obj) { return switch (obj) { case Integer i -> String.format("int %d", i); case Long l -> String.format("long %d", l); case Double d -> String.format("double %f", d); case String s -> String.format("String %s", s); default -> obj.toString(); }; } static void testFooBar(String s) { switch (s) { case null -> System.out.println("Oops"); case "Foo", "Bar" -> System.out.println("Great"); default -> System.out.println("Ok"); } } }
public class VirtualThreadsDemo { /** * 基于8个线程池实现的虚拟线程 * 执行10000个任务,每个任务耗时100毫秒,总共耗费3515毫秒 */ public static void virtualThread(int count) throws InterruptedException { ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor(); StopWatcher stopWatcher = new StopWatcher(); stopWatcher.start(); CountDownLatch countDownLatch = new CountDownLatch(count); for (int i = 0; i < count; i++) { executorService.submit(new TestRunner(countDownLatch)); // CompletableFuture.runAsync(new TestRunner(countDownLatch), Executors.newVirtualThreadPerTaskExecutor()); } countDownLatch.await(); stopWatcher.stop(); System.out.printf("本次执行耗时:%s毫秒", stopWatcher.getTimeInterval().toMillis()); } /** * 基于7个池化线程 * 执行一万个任务,每个任务耗时100毫秒 156459毫秒 */ public static void platformThread(int count) throws InterruptedException { StopWatcher stopWatcher = new StopWatcher(); stopWatcher.start(); CountDownLatch countDownLatch = new CountDownLatch(count); for (int i = 0; i < count; i++) { CompletableFuture.runAsync(new TestRunner(countDownLatch)); } countDownLatch.await(); stopWatcher.stop(); System.out.printf("本次执行耗时:%s毫秒", stopWatcher.getTimeInterval().toMillis()); } public static void main(String[] args) throws Exception { // 虚拟线程 // virtualThread(10_000); // 平台线程 platformThread(10_000); } public static class TestRunner implements Runnable { private final CountDownLatch countDownLatch; public TestRunner(CountDownLatch countDownLatch) { this.countDownLatch = countDownLatch; } @Override public void run() { try { // System.out.println(Thread.currentThread() + " start " + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())); Thread.sleep(100); // System.out.println(Thread.currentThread() + " stop " + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date())); countDownLatch.countDown(); // 未命名模式和变量 } catch (Exception _) { System.out.println("An error has occurred!"); } } } public static class StopWatcher { private long start; private long stop; public StopWatcher() { } public void start() { this.start = System.currentTimeMillis(); } public void stop() { this.stop = System.currentTimeMillis(); } public Duration getTimeInterval() { return Duration.ofMillis(this.stop - this.start); } } }
他强由他强,清风拂山冈;
他横由他横,明月照大江;
他发任他发,我用Java8;
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