How do I define constructor in enum type?

By Wayan 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 Wayan 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;
    }
}

How do I create enumerations type?

By Wayan in Basic, Core API 0 Comment

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.

How do I create an inner class?

By Wayan in Basic, Core API 0 Comment

An inner class is a class defined inside another class. Inner classes can, in fact, be constructed in several contexts. An inner class defined as a member of a class can be instantiated anywhere in that class. An inner class defined inside a method can only be referred to later in the same method. Inner classes can also be named or anonymous.

package org.kodejava.basic;

public class InnerClassDemo {
    private Bean bean;

    /**
     * Inner class, the compiled class will be named InnerClassDemo$Bean.class
     */
    class Bean {
        public int width;
        public int height;

        @Override
        public String toString() {
            return width + " x " + height;
        }
    }

    public InnerClassDemo() {
        Bean bean = new Bean();
        bean.width = 100;
        bean.height = 200;

        this.bean = bean;
    }

    public Bean getBean() {
        return this.bean;
    }

    public static void main(String[] args) {
        InnerClassDemo inner = new InnerClassDemo();
        System.out.println("inner.getBean() = " + inner.getBean());
    }
}

How do I clone an object?

By Wayan in Basic, Core API 0 Comment

To enable our object to be cloned we need to override Object class clone method. We can also add a java.lang.Cloneable interface to our class, this interface is an empty interface. When we call the clone() method we need the add a try-catch block to catch the CloneNotSupportedException. This exception will be thrown if we tried to clone an object that doesn’t suppose to be cloned.

Calling the clone() method does a stateful, shallow copy down inside the Java Virtual Machine (JVM). It creates a new object and copies all the fields from the old object into the newly created object.

package org.kodejava.basic;

public class CloneDemo implements Cloneable {
    private int number;
    private transient int data;

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

    public static void main(String[] args) {
        CloneDemo clone = new CloneDemo();
        clone.number = 5;
        clone.data = 1000;

        try {
            // Create a clone of CloneDemo object. When we change the value of
            // number and data field in the cloned object it won't affect the
            // original object.
            CloneDemo objectClone = (CloneDemo) clone.clone();
            objectClone.number = 10;
            objectClone.data = 5000;

            System.out.println("cloned object = " + objectClone);
            System.out.println("origin object = " + clone);
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }

    public String toString() {
        return "[number = " + number + "; data = " + data + "]";
    }
}