// enumerations/SealedPatternMatch.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// {NewFeature} Preview in JDK 17
// Compile with javac flags:
//   --enable-preview --source 17
// Run with java flag: --enable-preview
import java.util.*;

sealed interface Transport {};
record Bicycle(String id) implements Transport {};
record Glider(int size) implements Transport {};
record Surfboard(double weight) implements Transport {};
// If you uncomment this:
// record Skis(int length) implements Transport {};
// You get an error: "the switch expression
// does not cover all possible input values"

public class SealedPatternMatch {
  static String exhaustive(Transport t) {
    return switch(t) {
      case Bicycle b -> "Bicycle " + b.id();
      case Glider g -> "Glider " + g.size();
      case Surfboard s -> "Surfboard " + s.weight();
    };
  }
  public static void main(String[] args) {
    List.of(
      new Bicycle("Bob"),
      new Glider(65),
      new Surfboard(6.4)
    ).forEach(
      t -> System.out.println(exhaustive(t))
    );
    try {
      exhaustive(null); // Always possible!  // [1]
    } catch(NullPointerException e) {
      System.out.println("Not exhaustive: " + e);
    }
  }
}
/* Output:
Bicycle Bob
Glider 65
Surfboard 6.4
Not exhaustive: java.lang.NullPointerException
*/