// 传统写法 - 需要命名未使用的变量
try {int result = Integer.parseInt(input);
} catch (NumberFormatException e) { // e未使用System.out.println("Invalid number");
}// Java 22新写法
try {int result = Integer.parseInt(input);
} catch (NumberFormatException _) { // 使用_忽略异常参数System.out.println("Invalid number");
}

// 传统instanceof检查
if (obj instanceof String s) {System.out.println(s.length()); // 可能不需要s变量
}// Java 22改进
if (obj instanceof String _) { // 仅检查类型不绑定变量System.out.println("It's a String");
}

// 传统字符串拼接
String name = "Alice";
String message = "Hello " + name + ", your balance is $" + balance;// Java 22字符串模板
String message = STR."Hello \{name}, your balance is \$\{balance}";// 多行模板
String json = STR."""{"name": "\{name}","balance": \{balance}}""";

// 创建SQL安全模板
String query = SQL."""SELECT * FROM users WHERE name = \{name} AND age > \{minAge}""";// 处理器实现示例
class SQLTemplateProcessor implements TemplateProcessor<String> {public String process(Template template) {// 实现参数转义等安全处理return buildSafeQuery(template);}
}

// Java 21基础API
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {Future<String> user = scope.fork(() -> fetchUser());Future<Integer> order = scope.fork(() -> fetchOrder());scope.join();return new Response(user.resultNow(), order.resultNow());
}// Java 22改进 - 结果收集器
try (var scope = new StructuredTaskScope.Collector<Result>()) {scope.fork(() -> fetchDataA());scope.fork(() -> fetchDataB());return scope.join().stream().map(Future::resultNow).collect(Collectors.toList());
}

// 新的调度器配置
ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor().withScheduler(new WorkStealingScheduler(4)); // 指定调度策略// 自定义虚拟线程属性
Thread.Builder builder = Thread.ofVirtual().name("worker-", 0).scheduler(customScheduler).allowSetThreadLocals(false);

// 嵌套记录解构
record Point(int x, int y) {}
record Rectangle(Point topLeft, Point bottomRight) {}void printArea(Object obj) {if (obj instanceof Rectangle(Point(var x1, var y1), Point(var x2, var y2))) {System.out.println(Math.abs((x2-x1)*(y2-y1)));}
}

// 编译器检查模式覆盖
sealed interface Shape permits Circle, Rectangle, Triangle {}String describe(Shape s) {return switch (s) { // 编译器确保所有子类型被处理case Circle _ -> "Round";case Rectangle _ -> "Angular";case Triangle _ -> "Pointy";};
}

// 不可变集合创建
List<String> names = List.of("a", "b", "c");
Set<Integer> codes = Set.of(404, 500, 200);// Java 22新增 - 从流创建
List<String> filtered = Stream.of("a", "b", "c").filter(s -> s.length() == 1).toList(); // 直接转为不可变列表

// 新的向量API（JEP 460）
var a = FloatVector.fromArray(FloatVector.SPECIES_256, floats, 0);
var b = FloatVector.fromArray(FloatVector.SPECIES_256, floats, 8);
var c = a.mul(b).add(b);// 高精度计算增强
BigDecimal result = BigDecimal.valueOf(2).sqrt(MathContext.DECIMAL128).plus() // 新方法.round(new MathContext(10));

// 提案中的语法
value class Point {int x;int y;Point(int x, int y) {this.x = x;this.y = y;}
}// 使用效果
Point p = new Point(1, 2);
System.out.println(p.x()); // 自动访问方法

// 简化工具类定义
implicit class StringOps {public String repeat(String s, int n) {return s.repeat(n);}
}// 自动扩展方法
"Java".repeat(3); // 编译为StringOps.repeat("Java", 3)

# 编译时启用预览特性
javac --release 22 --enable-preview Main.java
java --enable-preview Main

// 兼容Java 21和22的代码模式
public final class StringUtils {@SuppressWarnings("preview")public static String greet(String name) {return STR."Hello, \{name}!";}
}

graph LR
A[Java 21] --> B[未命名变量]
A --> C[字符串模板]
A --> D[结构化并发]
B --> E[模式匹配]
C --> F[自定义模板]

// 传统代码
String sql = "SELECT * FROM users WHERE id = " + id;// 迁移为
String sql = SQL."SELECT * FROM users WHERE id = \{id}";

// 更简洁的异常处理
try { ... } catch (IOException _) { ... }

// 更强大的模式匹配
if (obj instanceof Point(int x, _)) { ... }

// 结构化并发成为标准
try (var scope = new StructuredTaskScope<Variant>()) { ... }