What Is an Enum Type

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∟What Is an Enum Type

This section describes 'enum' types, which are defined by 'enum' declaration statements. An 'enum' type is actually a special kind of class type.

What Is an Enum Type? An enum type is a special kind of class type that has a set of pre-defined instances representing a set of static values called enum constants.

An enum type is defined by the "enum" declaration statement. A simplest enum Type can be defined with 2 components:

The enum type name - Specified by the declaration identifier.
The enum constant list - Specified as a comma-delimited identifier list in the declaration body.

Here is an example of "enum" declaration statement:

/* Color.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
enum Color {
   // enum constants declaration and initialization
   RED, GREEN, BLUE;
}

The above "enum" declaration statement actually:

Defines a class called "Color".
Declares 3 public static variables: "RED", "GREEN", and "BLUE".
Creates one "Color" instance assigned to each variable listed above.
Overrides the toString() instance method to return its associated variable name.

We can verify the above with this test program:

/* ColorTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
class ColorTest {
   public static void main(String[] arg) {

      System.out.println("Converting enum constant to string:");
      System.out.println("   Color.RED = "+Color.RED);
      System.out.println("   Color.GREEN = "+Color.GREEN);
      System.out.println("   Color.BLUE = "+Color.BLUE);

      System.out.println("Getting enum constant class name:");
      String clsName = Color.RED.getClass().getName();
      System.out.println("   Color.RED.getClass().getName() = "+clsName);
   }
}

If you compile ColorTest.java with Color.java and run ColorTest.class, you should get:

herong> javac Color.java

herong> javac ColorTest.java

herong> java ColorTest
Converting enum constant to string:
   Color.RED = RED
   Color.GREEN = GREEN
   Color.BLUE = BLUE
Getting enum constant class name:
   Color.RED.getClass().getName() = Color