Inheritance on an Enum in Java

1. Use enums in Java
2. Java enum Inheritance
3. Use an enum to Implement an Interface

In Java, an enum (short form for enumeration) is a data type with a fixed constant value set. We use the enum keyword to declare the enumeration data type.

It is a common practice to represent enum values in uppercase. In Java, all the enum classes are final by default.

So, we cannot inherit or derive different classes from it.

Use enums in Java

enum Seasons
{
   SUMMER, WINTER, AUTUMN, SPRING
}

class Main
{
   public static void main(String[] args)
   {

      System.out.println(Seasons.SUMMER);
      System.out.println(Seasons.WINTER);
      System.out.println(Seasons.AUTUMN);
      System.out.println(Seasons.SPRING);
   }
}

Output:

SUMMER
WINTER
AUTUMN
SPRING

The above code displays the functionality of an enum data type. The use of enums can make any code more explicit and less error-prone.

Enums are widely used in menu-driven programs or when we know all possible values at compile time.

Java enum Inheritance

enum Seasons
{
   SUMMER, WINTER, AUTUMN, SPRING
}

class Main
{
class Weather extends Seasons
{
  public static void main(String[] args)
  {
    // statements
  }
}
}

Output:

Main.java:8: error: cannot inherit from final Seasons
class Weather extends Seasons {
                      ^
Main.java:8: error: enum types are not extensible
class Weather extends Seasons {
^

The above code produces an error because an enum class cannot be used to derive another functional class.

Use an enum to Implement an Interface

interface Weather {
 public void display();
}

enum Seasons implements Weather
{
   SUMMER, WINTER, AUTUMN, SPRING;
    public void display()
    {
    System.out.println("The season is " + this);
 }
}

class Main
{
   public static void main(String[] args)
   {
      Seasons.SUMMER.display();
   }
}

Output:

The season is SUMMER

In the above code, we are using an enum class, Seasons, to implement the Weather interface. Since we can use an enum class to implement an interface, we have written the abstract method display() inside the enum class.