Introduction to Enums

Input/Output and Streams in Java

Alex Liu

Software Development Engineer

Why Use Enums?

Enums define a fixed set of values
- Example: Days of the week, Status codes
Improves code readability and maintainability
Prevents invalid values in variables
Notes: No import is needed, as Enums are part of core Java library

Defining an Enum

Declare an Enum using enum keyword

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

Each value is a constant and written in uppercase

Using Enums in a program

Example: Assign and print an Enum value

public class EnumExample {
  public static void main(String[] args) {
      Day today = Day.WEDNESDAY; // Assigning an Enum value
      System.out.println("Today is: " + today);
  }
}

Output:
```
Today is: WEDNESDAY
```

Looping through Enum values

Use .values() to get all values in an Enum
Use .ordinal() return the position of the element

Lets reuse the previous defined Day Enum as an example:

for (Day d : Day.values()) {
  System.out.println(d);
  System.out.print(
  " is at index " + d.ordinal());
}

This program will output all the values defined in the Enum:

MONDAY is at index 0
TUESDAY is at index 1
WEDNESDAY is at index 2
THURSDAY is at index 3
FRIDAY is at index 4
SATURDAY is at index 5
SUNDAY is at index 6

Enum with methods

Enums can have methods for additional functionality

enum Status {
    SUCCESS("Operation successful"),
    ERROR("An error occurred");

    private String message;
    Status(String message) {
        this.message = message;
    }
    public String getMessage() {
        return message;
    }
}

Enum with methods

Example usage of Enum named Status

public class EnumMethodExample {
    public static void main(String[] args) {
        Status current = Status.SUCCESS;
        System.out.println("Status: " + current);
        System.out.println("Message: " + current.getMessage());
    }
}

Output:

Status: SUCCESS
Message: Operation successful

Let's practice!

Input/Output and Streams in Java