How do I get ordinal value of enum constant?

This example demonstrate the use of enum ordinal() method to get the ordinal value of an enum constant.

package org.kodejava.basic;

enum Color {
    RED, GREEN, BLUE
}

public class EnumOrdinal {
    public static void main(String[] args) {
        // Gets the ordinal of this enumeration constant (its
        // position in its enum declaration, where the initial 
        // constant is assigned an ordinal of zero)
        System.out.println("Color.RED  : " + Color.RED.ordinal());
        System.out.println("Color.GREEN: " + Color.GREEN.ordinal());
        System.out.println("Color.BLUE : " + Color.BLUE.ordinal());
    }
}

The program print the following result:

Color.RED  : 0
Color.GREEN: 1
Color.BLUE : 2

How do I define a field in enum type?

As we know that Java enumeration type is powerful compared to enum implementation in other programming language. Basically enum is class typed, so it can have constructors, methods and fields.

In the example below you’ll see how a field is defined in an enumeration type. Because each constant value for the Fruit enum is a type of Fruit itself it will have its own price field. The price field holds a unique value for each constant such as APPLE, ORANGE, etc.

In the result you’ll see that the constructor will be called for each constant value and initialize it with the value passed to the constructor.

package org.kodejava.basic;

enum Fruit {
    APPLE(1.5f), ORANGE(2), MANGO(3.5f), GRAPE(5);

    private final float price;

    Fruit(float price) {
        System.out.println("Name: " + this.name() + " initialized.");
        this.price = price;
    }

    public float getPrice() {
        return this.price;
    }
}

public class EnumFieldDemo {
    public static void main(String[] args) {
        // Get the name and price of all enum constant value.
        for (Fruit fruit : Fruit.values()) {
            System.out.printf("Fruit = %s; Price = %5.2f%n",
                    fruit.name(), fruit.getPrice());
        }
    }
}

Our demo result is below:

Name: APPLE initialized.
Name: ORANGE initialized.
Name: MANGO initialized.
Name: GRAPE initialized.
Fruit = APPLE; Price =  1.50
Fruit = ORANGE; Price =  2.00
Fruit = MANGO; Price =  3.50
Fruit = GRAPE; Price =  5.00

How do I get enum constant value corresponds to a string?

The valueOf() method of an enum type allows you to get an enum constant that the value corresponds to the specified string. Exception will be thrown when we pass a string that not available in the enum.

package org.kodejava.basic;

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}
package org.kodejava.basic;

public class EnumValueOfTest {
    public static void main(String[] args) {
        // Using valueOf() method we can get an enum constant whose
        // value corresponds to the string passed as the parameter.
        Day day = Day.valueOf("SATURDAY");
        System.out.println("Day = " + day);
        day = Day.valueOf("WEDNESDAY");
        System.out.println("Day = " + day);

        try {
            // The following line will produce an exception because the
            // enum type does not contain a constant named JANUARY.
            day = Day.valueOf("JANUARY");
            System.out.println("Day = " + day);
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        }
    }
}

The output of the code snippet above:

Day = SATURDAY
Day = WEDNESDAY
java.lang.IllegalArgumentException: No enum constant org.kodejava.basic.Day.JANUARY
    at java.base/java.lang.Enum.valueOf(Enum.java:273)
    at org.kodejava.basic.Day.valueOf(Day.java:3)
    at org.kodejava.basic.EnumValueOfTest.main(EnumValueOfTest.java:15)

How do I get constants name of an enum?

To get the constants name of an enumeration you can use the values() method of the enumeration type. This method return an array that contains a list of enumeration constants.

package org.kodejava.basic;

public enum Month {
    JANUARY,
    FEBRUARY,
    MARCH,
    APRIL,
    MAY,
    JUNE,
    JULY,
    AUGUST,
    SEPTEMBER,
    OCTOBER,
    NOVEMBER,
    DECEMBER
}
package org.kodejava.basic;

public class EnumValuesTest {
    public static void main(String[] args) {
        // values() method return an array that contains a list of the
        // enumeration constants.
        Month[] months = Month.values();
        System.out.println("Month size: " + months.length);

        // We can use for each statement to print each enumeration
        // constant.
        for (Month month : Month.values()) {
            System.out.println("Month: " + month);
        }
    }
}

How do I create enumerations type?

Enumeration is a list of named constants. Every most commonly used programming languages support this feature. But in Java it is officially supported since version 5.0. In Java programming language an enumeration defines a class type. Because an enumeration is a class it can have a constructors, methods, and instance variables.

To create an enumeration we use the enum keyword. For example below is a simple enumeration that hold a list of notebook producers:

package org.kodejava.basic;

public enum Producer {
    ACER, APPLE, DELL, FUJITSU, LENOVO, TOSHIBA
}

Below we use our enumeration in a simple program.

package org.kodejava.basic;

public class EnumDeclaration {
    public static void main(String[] args) {
        // Creates an enum variable declaration and assign the value to
        // Producer.APPLE.
        Producer producer = Producer.APPLE;

        if (producer == Producer.LENOVO) {
            System.out.println("Produced by Lenovo.");
        } else {
            System.out.println("Produced by others.");
        }
    }
}

The ACER, APPLE, DELL identifiers are called enumeration constants. Every named constants have an implicitly assigned public and static access modifiers. Although the enumeration is a class type, to create an enumeration variable we don’t use the new keyword. We create an enum just like creating a primitive type of data, as you can see in the example above.