Enhancements in Java 增强特性

  • Z时代
  • 2024-01-10
  • 分类：综合

java

Enhancements in Java 增强特性，Java Language Changes for Java SE 9，分别介绍了Java 5至Java 9的增强特性，这里继续介绍后续版本的新特性。

JDK 10：移除了javah

  • 286：Local-Variable Type Inference，本地变量类型推断
    var list = new ArrayList<String>();  // infers ArrayList<String>
    var stream = list.stream();          // infers Stream<String>

JDK11：2018/09/25，移除了javaee和corba，支持TLS 1.3，废弃Nashorn和Pack200

  • 321：Http Client，http客户端，intro
    HttpClient client = HttpClient.newHttpClient();
    HttpRequest request = HttpRequest.newBuilder()
          .uri(URI.create(http://openjdk.java.net/))
          .timeout(Duration.ofMinutes(1))
          .header("Content-Type", "application/json")
          .POST(BodyPublishers.ofFile(Paths.get("file.json")))
          .build();
    HttpResponse<String> response = client.send(request, BodyHandlers.ofString());
    client.sendAsync(request, BodyHandlers.ofString())
          .thenApply(response -> { System.out.println(response.statusCode()); return response; } )
          .thenApply(HttpResponse::body)
          .thenAccept(System.out::println);
    //BodyPublishers::ofByteArray(byte[]) ofString(String) ofInputStream(Supplier<InputStream>)
    //BodyHandlers::ofByteArray() ofFile(Path) discarding()

  • 323：Local-Variable Syntax for Lambda Parameters
    (var x, var y) -> x.process(y)

  • 330：Launch Single-File Source-Code Programs，执行单源码文件
    java HelloWorld.java

JDK12：

  • 325：Switch Expressions (Preview)，多条语句时使用花括号和break
    int numLetters = switch (day) {
         case MONDAY, FRIDAY, SUNDAY -> 6;
         case TUESDAY                -> 7;
         case THURSDAY, SATURDAY     -> 8;
         case WEDNESDAY              -> { break 9; }

    };

JDK13：改进Socket，

  • 354：Switch Expressions (Second Preview)，使用yield（替代break）返回值
    int i = switch(day){
      default –> yield 0;
    }

  • 355：Text Blocks (Preview)，文本块适用于html、sql、javascript等
    String html = """
                   <html>
                       <body>
                           <p>Hello, world</p>
                       </body>
                   </html>
                   """;

    String query = """
                    SELECT `EMP_ID`, `LAST_NAME` FROM `EMPLOYEE_TB`
                    WHERE `CITY` = 'INDIANAPOLIS'
                    ORDER BY `EMP_ID`, `LAST_NAME`;
                    """;
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("js");

    Object obj = engine.eval("""
                              function hello() {
                                  print('"Hello, world"');
                              }
                             
                              hello();
                              """);

JDK14：2020/03/17，新增jpackage，转正switch，移除Pack200，

  • 305：Pattern Matching for instanceof (Preview)，类型判断并声明变量
    if (obj instanceof String s && s.length() > 5) {
         // can use s here s.contains(..)

    } else {
         // can't use s here

    }

    @Override public boolean equals(Object o) {
         return (o instanceof CaseInsensitiveString cis) &&
             cis.s.equalsIgnoreCase(s);

    }

  • 358：Helpful NullPointerExceptions
    a.i = 99; //a为null时错误信息更加详细

    Exception in thread "main" java.lang.NullPointerException:
             Cannot assign field "i" because "a" is null
         at Prog.main(Prog.java:5)

  • 359：Records (Preview)，替代lombok，自动提供方法getter constructor equals hashCode toString，不可变更对象
    record Point(int x, int y) { }

    boolean Class#isRecord()

  • 370：Foreign-Memory Access API (Incubator)，堆外内存访问
    VarHandle intHandle = MemoryHandles.varHandle(int.class,
             ByteOrder.nativeOrder());

    VarHandle intElemHandle = MemoryHandles.withStride(intHandle, 4);

    try (MemorySegment segment = MemorySegment.allocateNative(100)) {
         MemoryAddress base = segment.baseAddress();
         for (int i = 0; i < 25; i++) {
             intElemHandle.set(base, (long) i, i);
         }

    }

JDK15：移除Nashorn，改进DatagramSocket，

  • 339：Edwards-Curve Digital Signature Algorithm (EdDSA)

  • 360：Sealed Classes (Preview)

  • 371：Hidden Classes

JDK16：支持C++14语法，迁移至GitHub，

  • 338：Vector API (Incubator)

以上是 Enhancements in Java 增强特性 的全部内容， 来源链接： utcz.com/z/389723.html

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