Java enum Keyword

The enum keyword in Java is used to define a special class that represents a group of constants. Enums are a powerful feature for creating a fixed set of related constants with type safety. Each enum constant is an instance of the enum class.

Table of Contents

1. Introduction
2. enum Keyword Syntax
3. Understanding Enums
4. Examples
   • Basic Enum
   • Enum with Fields and Methods
   • Using Enums in Switch Statements
5. Real-World Use Case
6. Conclusion

Introduction

Enums in Java are used to represent a fixed set of constants. They provide a way to define a collection of related values in a type-safe manner. Enums can also have fields, methods, and constructors, making them more powerful than simple constants.

enum Keyword Syntax

The syntax for defining an enum is as follows:

enum EnumName {
    CONSTANT1,
    CONSTANT2,
    CONSTANT3
}

Example:

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

Understanding Enums

Enums can be used to define a collection of constants. Each constant is an instance of the enum type. Enums can also include fields, methods, and constructors to add more functionality.

Key Points:

• Enums provide type safety.
• Enums can have fields, methods, and constructors.
• Enums can implement interfaces but cannot extend classes.
• The enum constants are implicitly public, static, and final.

Examples

Basic Enum

A basic example of an enum to represent days of the week.

Example

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

public class Main {
    public static void main(String[] args) {
        Day today = Day.WEDNESDAY;
        System.out.println("Today is: " + today);
    }
}

Output:

Today is: WEDNESDAY

Enum with Fields and Methods

Enums can have fields, methods, and constructors to add more functionality.

Example

enum Day {
    SUNDAY("Sun"),
    MONDAY("Mon"),
    TUESDAY("Tue"),
    WEDNESDAY("Wed"),
    THURSDAY("Thu"),
    FRIDAY("Fri"),
    SATURDAY("Sat");

    private String abbreviation;

    Day(String abbreviation) {
        this.abbreviation = abbreviation;
    }

    public String getAbbreviation() {
        return abbreviation;
    }
}

public class Main {
    public static void main(String[] args) {
        Day today = Day.WEDNESDAY;
        System.out.println("Today is: " + today);
        System.out.println("Abbreviation: " + today.getAbbreviation());
    }
}

Output:

Today is: WEDNESDAY
Abbreviation: Wed

Using Enums in Switch Statements

Enums can be used in switch statements for better readability and type safety.

Example

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

public class Main {
    public static void main(String[] args) {
        Day today = Day.WEDNESDAY;

        switch (today) {
            case MONDAY:
                System.out.println("Start of the work week.");
                break;
            case WEDNESDAY:
                System.out.println("Midweek.");
                break;
            case FRIDAY:
                System.out.println("End of the work week.");
                break;
            default:
                System.out.println("Weekend.");
                break;
        }
    }
}

Output:

Midweek.

Real-World Use Case

Defining Error Codes

Enums can be used to define a set of error codes in an application.

Example

enum ErrorCode {
    NOT_FOUND(404, "Not Found"),
    INTERNAL_SERVER_ERROR(500, "Internal Server Error"),
    BAD_REQUEST(400, "Bad Request");

    private int code;
    private String description;

    ErrorCode(int code, String description) {
        this.code = code;
        this.description = description;
    }

    public int getCode() {
        return code;
    }

    public String getDescription() {
        return description;
    }
}

public class Main {
    public static void main(String[] args) {
        ErrorCode error = ErrorCode.NOT_FOUND;
        System.out.println("Error Code: " + error.getCode() + ", Description: " + error.getDescription());
    }
}

Output:

Error Code: 404, Description: Not Found

Conclusion

The enum keyword in Java provides a powerful way to define a collection of constants with additional functionality. Enums are type-safe and can have fields, methods, and constructors. By understanding and using enums, you can create more readable and maintainable code, especially when dealing with fixed sets of related constants.