Prompting ChatGPT: Create a Java interview question, where using enum is the best solution

java-interview-question-usuing-enum.md

ChatGPT:

Java Interview Question:

Question:
You are designing a system that processes customer orders. Each order has a status that can change over time. The possible statuses are:

• NEW (Order just created)
• PROCESSING (Currently being processed)
• SHIPPED (Sent to the customer)
• DELIVERED (Received by the customer)
• CANCELLED (Order was cancelled)

Each status has the following behavior:

1. Some statuses can transition only to specific other statuses.
2. Each status should have a method canTransitionTo(OrderStatus nextStatus) that validates if the transition is allowed.
3. Each status should have a getDisplayName() method to return a user-friendly name.

Question Tasks:

1. Implement the OrderStatus in the most efficient way.
2. Ensure that invalid transitions are prevented.
3. Provide a simple test case to demonstrate how an order changes status correctly.

---

This question naturally leads to using an enum because:

• Enums provide a fixed set of constants, perfect for representing statuses.
• Enums can have methods and fields, making them ideal for defining transition rules.
• Enums improve code readability and maintainability compared to using plain integers or strings.

Would you like a sample implementation for this? 😊

---

prompt: yes

ChatGPT:

Here’s an implementation using an enum to handle order statuses efficiently:

Implementation of OrderStatus Enum

public enum OrderStatus {
    NEW("New Order") {
        @Override
        public boolean canTransitionTo(OrderStatus nextStatus) {
            return nextStatus == PROCESSING || nextStatus == CANCELLED;
        }
    },
    PROCESSING("Processing Order") {
        @Override
        public boolean canTransitionTo(OrderStatus nextStatus) {
            return nextStatus == SHIPPED || nextStatus == CANCELLED;
        }
    },
    SHIPPED("Shipped Order") {
        @Override
        public boolean canTransitionTo(OrderStatus nextStatus) {
            return nextStatus == DELIVERED;
        }
    },
    DELIVERED("Delivered Order") {
        @Override
        public boolean canTransitionTo(OrderStatus nextStatus) {
            return false; // Final status, cannot transition further
        }
    },
    CANCELLED("Cancelled Order") {
        @Override
        public boolean canTransitionTo(OrderStatus nextStatus) {
            return false; // Cannot transition from a cancelled order
        }
    };

    private final String displayName;

    OrderStatus(String displayName) {
        this.displayName = displayName;
    }

    public String getDisplayName() {
        return displayName;
    }

    // Abstract method to enforce transition logic in each enum constant
    public abstract boolean canTransitionTo(OrderStatus nextStatus);
}

---

Using the OrderStatus Enum in an Order Class

public class Order {
    private OrderStatus status;

    public Order() {
        this.status = OrderStatus.NEW;
    }

    public boolean changeStatus(OrderStatus newStatus) {
        if (status.canTransitionTo(newStatus)) {
            this.status = newStatus;
            System.out.println("Order status changed to: " + status.getDisplayName());
            return true;
        } else {
            System.out.println("Invalid transition from " + status + " to " + newStatus);
            return false;
        }
    }

    public OrderStatus getStatus() {
        return status;
    }
}

---

Test Case

public class OrderStatusTest {
    public static void main(String[] args) {
        Order order = new Order();
        System.out.println("Initial Status: " + order.getStatus());

        order.changeStatus(OrderStatus.PROCESSING); // Valid transition
        order.changeStatus(OrderStatus.SHIPPED);    // Valid transition
        order.changeStatus(OrderStatus.DELIVERED);  // Valid transition
        order.changeStatus(OrderStatus.CANCELLED);  // Invalid transition (should fail)
    }
}

---

Expected Output

Initial Status: NEW
Order status changed to: Processing Order
Order status changed to: Shipped Order
Order status changed to: Delivered Order
Invalid transition from DELIVERED to CANCELLED

---

Why Use an Enum Here?

✅ Ensures type safety – No invalid values can be assigned.
✅ Encapsulates logic – Each status defines its own transition rules.
✅ Readability & Maintainability – Clear, structured, and easy to modify.
✅ Performance – Enums are more efficient than using a Map or multiple if-else statements.

Would you like to extend this with additional features, like tracking the history of status changes? 😊