How do I define a field in enum type?

By I Wayan Saryada in Basic, Core API 0 Comment

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?

By I Wayan Saryada in Basic, Core API 0 Comment

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?

By I Wayan Saryada in Basic, Core API 0 Comment

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 define constructor in enum type?

By I Wayan Saryada in Basic, Core API 0 Comment

In the following example you’ll see how to add a constructor to an enum type value. Because an enum is just another class type it can have constructors, fields and methods just like any other classes. Below we define a constructor that accept a string value of color code. Because our enum now have a new constructor declared we have to define the constant named value as RED("FF0000"), ORANGE("FFA500"), etc.

In Java enumeration expanded beyond just as a named constants. Because enum is a class type we can add methods, fields and constructors to the enum type as you can see in the example below.

package org.kodejava.basic;

public enum Rainbow {
    RED("FF0000"),
    ORANGE("FFA500"),
    YELLOW("FFFF00"),
    GREEN("008000"),
    BLUE("0000FF"),
    INDIGO("4B0082"),
    VIOLET("EE82EE");

    private final String colorCode;

    // The constructor of Rainbow enum.
    Rainbow(String colorCode) {
        this.colorCode = colorCode;
    }

    /**
     * Get the hex color code.
     *
     * @return hex color code
     */
    public String getColorCode() {
        return colorCode;
    }
}

package org.kodejava.basic;

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

        // To get all values of the Rainbow enum we can call the
        // Rainbow.values() method which return an array of
        // Rainbow enum values.
        for (Rainbow color : Rainbow.values()) {
            System.out.println("Color = " + color.getColorCode());
        }
    }
}

How do I use enum in switch statement?

By I Wayan Saryada in Basic, Core API 0 Comment

This example show you how to use enumeration or enum type in a switch statement.

package org.kodejava.basic;

public enum RainbowColor {
    RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO, VIOLET
}

package org.kodejava.basic;

public class EnumSwitch {
    public static void main(String[] args) {
        RainbowColor color = RainbowColor.INDIGO;

        EnumSwitch es = new EnumSwitch();
        String colorCode = es.getColorCode(color);
        System.out.println("ColorCode = #" + colorCode);
    }

    public String getColorCode(RainbowColor color) {
        String colorCode = "";

        // We use the switch-case statement to get the hex color code of our
        // enum type rainbow colors. We can pass the enum type as expression
        // in the switch. In the case statement we only use the enum named
        // constant excluding its type name.
        switch (color) {
            // We use RED instead of RainbowColor.RED
            case RED -> colorCode = "FF0000";
            case ORANGE -> colorCode = "FFA500";
            case YELLOW -> colorCode = "FFFF00";
            case GREEN -> colorCode = "008000";
            case BLUE -> colorCode = "0000FF";
            case INDIGO -> colorCode = "4B0082";
            case VIOLET -> colorCode = "EE82EE";
        }
        return colorCode;
    }
}