Abstract Data Type / Sum type / Discriminated union for java

adt.java

// from https://github.com/cboudereau/adt-java17-presentation > https://github.com/fteychene/adt-java17-presentation

package com.example;

public class App {

    public enum Direction {
        NORTH,
        SOUTH,
        EAST,
        WEST
    }

    public record Chain(Command a, Command b) implements Command {
    }

    public record Cute() implements Command {
    }

    public record Move(Integer steps) implements Command {
    }

    public record TakeOver() implements Command {
    }

    public record Turn(Direction direction) implements Command {
    }

    public sealed interface Command permits Chain, Cute, Move, TakeOver, Turn {

        default Command then(Command next) {
            return new Chain(this, next);
        }

    }

    public static void handle(Command command) {
        switch (command) {
            case Move m -> display("Move of " + m.steps());
            case Turn t -> {
                switch (t.direction()) {
                    case NORTH -> display("Turning north");
                    case SOUTH -> display("Turning south");
                    case WEST -> display("Turning east");
                    case EAST -> display("Turning west");
                }
            }
            case Cute cute -> display("Do something cute no one can resist");
            case TakeOver takeOver -> display("Start taking over the WORLD !!!!!!!");
            case Chain chain -> {
                handle(chain.a());
                handle(chain.b());
            }
        }
    }

    public static void display(String message) {
        System.out.println("\uD83E\uDD16 : " + message);
    }

    public static void main(String[] args) {
        var command = new Chain(new Cute(), new Move(2));
        handle(command);
    }

}