Try Union Type In Java

TestSecureResource1.java

sealed interface Permission permits Read, Write {}
record Read() implements Permission {}
record Write() implements Permission {}

record Execute() {}

class ResourceAction {
  public String perform(Permission permission) {
    return String.format("Performing action with %s...", permission.getClass().getSimpleName());
  }
}

class TestSecureResource1 {
  public static void main(String[] args) {
    final var resourceAction = new ResourceAction();
    System.out.println(resourceAction.perform(new Read()));    // Performing action with Read...
    System.out.println(resourceAction.perform(new Write()));   // Performing action with Write...
    System.out.println(resourceAction.perform(new Execute())); /* Compilation Error!!!!
                                                                * Required type: Permission
                                                                * Provided: Execute
                                                                */
  }
}

TestSecureResource2.java

import java.lang.reflect.InvocationTargetException;
import java.util.Optional;

sealed interface Permission permits Read, Write {}
record Read() implements Permission {}
record Write() implements Permission {}

record Execute() {}

class Reflection {
  public static <T> Optional<T> createInstance(Class<T> clazz) {
    try {
      return Optional.of(clazz.getDeclaredConstructor().newInstance());
    } catch (InstantiationException
        | IllegalAccessException
        | InvocationTargetException
        | NoSuchMethodException e) {

      System.err.println("[WARN]: " + e.getMessage());
      return Optional.empty();
    }
  }
}

class ResourceAction {
  public static String perform(P permission) {
    return String.format("Performing action with %s...", permission.getClass().getSimpleName());
  }
}

class SecureResource {
  public <P extends Permission> String access(Class<P> permission) {
    return Reflection.createInstance(permission)
        .map(ResourceAction::perform)
        .orElseThrow(() -> new RuntimeException("Failed to instantiate Permission class"));
  }
}

class TestSecureResource2 {
  public static void main(String[] args) {
    final var resource = new SecureResource();

    System.out.println(resource.access(Read.class));    // Performing action with Read...
    System.out.println(resource.access(Write.class));   // Performing action with Write...
    System.out.println(resource.access(Execute.class)); /* Compilation Error!!!!
                                                         * No instance(s) of type variable(s) exist
                                                         * so that Execute conforms to Permission
                                                         */
  }
}