Explain enums in Java

💡 Concept: Enums in Java

Enums (enumerations) are a special data type in Java that enable variables to be a set of predefined constants.

📘 Quick Intro

Java enums are used to define collections of constants with type safety and better readability.

🧠 Analogy

Think of enums as a menu list in a restaurant where you can only choose from the items on the menu.

🔧 Technical Explanation

Enums are declared using the enum keyword.
Each enum constant is a static final instance of the enum type.
Enums can have fields, constructors, and methods.
Used to restrict variables to predefined values.
Improve code clarity and prevent invalid values.

🎯 Use Cases

✅ Represent fixed sets like days, months, directions.
✅ Use in switch statements for cleaner code.
✅ Enforce compile-time checking of valid values.

💻 Example: Enum Definition and Usage


public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY;
}

public class TestEnum {
    public static void main(String[] args) {
        Day today = Day.MONDAY;
        switch(today) {
            case MONDAY:
                System.out.println("Start of the work week");
                break;
            default:
                System.out.println("Other day");
        }
    }
}

❓ Interview Q&A

Q1: What is an enum in Java?
A: A special data type with fixed constants.

Q2: Can enums have methods?
A: Yes, they can have methods and fields.

Q3: How do you define an enum?
A: Using the enum keyword.

Q4: Are enums type-safe?
A: Yes.

Q5: Can enums be used in switch?
A: Yes.

Q6: Can enums implement interfaces?
A: Yes.

Q7: Can enums have constructors?
A: Yes, private constructors.

Q8: Are enum constants mutable?
A: No, they are final.

Q9: Can you get enum values as array?
A: Yes, using values() method.

Q10: Difference between enum and final constants?
A: Enums provide type safety and methods.

📝 MCQs

Q1. What is an enum in Java?

Fixed set of constants
Mutable class
Interface
Data type

Q2. Can enums have methods?

No
Yes
Sometimes
Depends

Q3. How do you define an enum?

Using class keyword
Using interface
Using enum keyword
Using final

Q4. Are enums type-safe?

No
Yes
Sometimes
Depends

Q5. Can enums be used in switch?

No
Yes
Maybe
Depends

Q6. Can enums implement interfaces?

No
Yes
Maybe
Depends

Q7. Can enums have constructors?

No
Yes
Maybe
Depends

Q8. Are enum constants mutable?

Yes
No
Sometimes
Depends

Q9. Can you get enum values as array?

No
Yes
Maybe
Depends

Q10. Difference between enum and final constants?

Same
Type safety and methods
Only constants
No difference

💡 Bonus Insight

Enums in Java provide a clean, type-safe way to represent fixed sets of constants with added flexibility.

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