🎌 Java Enums Explained – Syntax, Examples, EnumSet & EnumMap

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🧲 Introduction – Why Java Enums Matter

Imagine you’re building a game and need to define player levels: EASY, MEDIUM, HARD. You could use strings or integers — but what if someone accidentally sets level to “HARDD”? That’s where Java Enums shine.

Enums in Java provide a type-safe way to define a fixed set of constants. They are more powerful than enums in many other languages — because Java enums are full-fledged classes.

By the end of this article, you’ll understand:

✅ What enums are and how to define them
✅ How to add fields, methods, and constructors to enums
✅ Enum best practices and real-world examples
✅ EnumSet, EnumMap, and advanced use cases

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🔑 What is an Enum in Java?

🎌 An enum (short for “enumeration”) is a special Java type used to define a set of predefined constants.

📘 Java enums:

• Are type-safe
• Can have fields, methods, and constructors
• Can implement interfaces

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🧪 Basic Enum Syntax

enum Level {
    EASY,
    MEDIUM,
    HARD
}

public class TestEnum {
    public static void main(String[] args) {
        Level level = Level.MEDIUM;
        System.out.println("Selected level: " + level);
    }
}

✅ Output:

Selected level: MEDIUM

✅ Explanation:

• Level is an enum with 3 constants.
• Each constant (EASY, MEDIUM, HARD) is an object of Level.

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⚙️ Enum with Fields and Methods

enum Planet {
    MERCURY(3.30), VENUS(4.87), EARTH(5.97);

    private double mass; // in 10^24 kg

    Planet(double mass) {
        this.mass = mass;
    }

    public double getMass() {
        return mass;
    }
}

public class TestPlanet {
    public static void main(String[] args) {
        for (Planet p : Planet.values()) {
            System.out.println(p + " mass = " + p.getMass());
        }
    }
}

✅ Explanation:

• Each enum constant can hold associated data
• Enums can have constructors and methods
• Planet.values() returns an array of all enum constants

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🧰 Common Enum Methods

Method	Description
values()	Returns array of all enum constants
ordinal()	Returns the index of the constant (starts at 0)
name()	Returns the name of the constant as a string
valueOf("NAME")	Returns the enum constant by name

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🔁 Enum in Switch Statement

enum Day { MONDAY, TUESDAY, FRIDAY }

public class TestDay {
    public static void main(String[] args) {
        Day d = Day.FRIDAY;

        switch (d) {
            case MONDAY:
                System.out.println("Start of week");
                break;
            case FRIDAY:
                System.out.println("Weekend incoming!");
                break;
            default:
                System.out.println("Midweek");
        }
    }
}

✅ Enums work seamlessly with switch — providing clarity and readability

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🔄 EnumSet and EnumMap

✅ EnumSet Example

import java.util.EnumSet;

enum Direction { NORTH, EAST, SOUTH, WEST }

public class TestSet {
    public static void main(String[] args) {
        EnumSet<Direction> directions = EnumSet.of(Direction.NORTH, Direction.EAST);
        System.out.println(directions);
    }
}

✅ EnumMap Example

import java.util.*;

enum Status { NEW, IN_PROGRESS, COMPLETED }

public class TestMap {
    public static void main(String[] args) {
        EnumMap<Status, String> statusMap = new EnumMap<>(Status.class);
        statusMap.put(Status.NEW, "Task Created");
        statusMap.put(Status.COMPLETED, "Task Done");

        System.out.println(statusMap);
    }
}

📘 Note:

• EnumSet is a highly efficient Set for enum types.
• EnumMap is a specialized Map with enums as keys.

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🧠 Best Practices for Java Enums

✅ Use enums instead of int or String constants for clarity and safety
✅ Use EnumSet or EnumMap for collections involving enums
✅ Prefer switch-case for enum-driven logic
✅ Group related values and logic inside the enum itself
⚠️ Don’t abuse enums for unrelated constants — use only when values are logically grouped

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✅ Summary

• Java enums are powerful and type-safe tools for defining constant values
• They support fields, methods, constructors, and even interfaces
• Used with switch, EnumSet, and EnumMap for clean, efficient logic
• Enums improve code readability, safety, and maintainability

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❓ FAQs – Java Enums

❓ Can Java enums have constructors?

Yes. Enum constructors are used to set fields for each constant, but they are private by default.

❓ Can enums implement interfaces?

Yes. Enums can implement interfaces (but cannot extend classes).

❓ What is the default type of Java enum constants?

Each enum constant is an instance of the enum class.

❓ Can enum constants override methods?

Yes. Each constant can have its own implementation of a method using constant-specific class bodies.

❓ Is enum a class in Java?

Yes. Under the hood, each enum is compiled into a class that extends java.lang.Enum.

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