使用记录模式（Record Patterns）增强Java编程语言，以解构记录值。可以嵌套记录模式和类型模式，以实现功能强大、声明性和可组合形式的数据导航和处理。
Record Patterns
该功能首次在 Java SE 19 中预览，在Java SE 20中发布第二次预览版，在此版本中成为永久性功能。这意味着它可以在任何为 Java SE 21 编译的程序中使用，而无需启用预览功能。
示例代码如下
package git.snippets.jdk21;
/**
* record 模式匹配增强
* 无须增加 --enable-preview参数
* @since 21
*/
public class RecordTest {
public static void main(String[] args) {
Points points = new Points(1, 2);
Line line = new Line(new Points(1, 2), new Points(3, 4));
printPoints(points);
printLine(line);
}
private static void printPoints(Object object) {
if (object instanceof Points(int x, int y)) {
System.out.println("jdk 19 object is a position, x = " + x + ", y = " + y);
}
if (object instanceof Points points) {
System.out.println("pre jdk 19 object is a position, x = " + points.x()
+ ", y = " + points.y());
}
switch (object) {
case Points position -> System.out.println("pre jdk 19 object is a position, x = " + position.x()
+ ", y = " + position.y());
default -> throw new IllegalStateException("Unexpected value: " + object);
}
switch (object) {
case Points(int x, int y) -> System.out.println(" jdk 19 object is a position, x = " + x
+ ", y = " + y);
default -> throw new IllegalStateException("Unexpected value: " + object);
}
}
public static void printLine(Object object) {
if (object instanceof Line(Points(int x1, int y1), Points(int x2, int y2))) {
System.out.println("object is a path, x1 = " + x1 + ", y1 = " + y1
+ ", x2 = " + x2 + ", y2 = " + y2);
}
switch (object) {
case Line(Points(int x1, int y1), Points(int x2, int y2)) ->
System.out.println("object is a path, x1 = " + x1 + ", y1 = " + y1
+ ", x2 = " + x2 + ", y2 = " + y2);
// other cases ...
default -> throw new IllegalStateException("Unexpected value: " + object);
}
}
}
record Points(int x, int y) {
}
record Line(Points from, Points to) {
}