How do I convert angle from radians to degrees?

By Wayan in Core API, Math 0 Comment

The example below show you how to convert an angle measured in radians into degrees and vice versa. We can use the Math.toDegrees() and Math.toRadians() method call to do the conversion.

package org.kodejava.math;

public class RadiansDegreeConversionExample {
    public static void main(String[] args) {
        double radians = 1.0d;
        double degrees = 45d;

        // Converts an angle measured in radians to an
        // approximately equivalent angle measured in
        // degrees.
        double toDegree = Math.toDegrees(radians);

        // Converts an angle measured in degrees to an
        // approximately equivalent angle measured in
        // radians.
        double toRadians = Math.toRadians(degrees);

        System.out.println("Radians " + radians + " in degrees  = " + toDegree);
        System.out.println("Degrees " + degrees + " in radians = " + toRadians);
    }
}

The result of the snippet above are:

Radians 1.0 in degrees  = 57.29577951308232
Degrees 45.0 in radians = 0.7853981633974483

How do I get the PI value?

By Wayan in Core API, Math 2 Comments

The number π is a mathematical constant, the ratio of a circle’s circumference to its diameter, commonly approximated as 3.14159. It has been represented by the Greek letter “π” since the mid-18th century, though it is also sometimes spelled out as “pi” (/paɪ/).

From: Wikipedia

The code snippet below show you how to obtain the PI value in Java. We use the Math.PI static field to get the value of PI.

package org.kodejava.math;

public class GetPiExample {
    public static void main(String[] args) {
        // The PI value represented by Math.PI
        System.out.println("PI = " + Math.PI);

        // Using the Math.PI to calculate area of a circle.
        double radius = 8;
        double circleArea = Math.PI * Math.pow(radius, 2);
        System.out.println("Circle Area = " + circleArea);
    }
}

Here is the program output:

PI = 3.141592653589793
Circle Area = 201.06192982974676

How do I get the minimum or maximum value between two numbers?

By Wayan in Core API, Math 0 Comment

The code below show you how to use the Math.min() and Math.max() method call the get the minimum and maximum value between two numbers. As other method in the Math class these methods also overloaded to accept many types of primitive data.

package org.kodejava.math;

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

        Double value1 = 100.0D;
        Double value2 = 200.0D;

        double max1 = Math.max(value1, value2);
        double min1 = Math.min(value1, value2);

        float max2 = Math.max(value1.floatValue(), value2.floatValue());
        float min2 = Math.min(value1.floatValue(), value2.floatValue());

        int max3 = Math.max(value1.intValue(), value2.intValue());
        int min3 = Math.min(value1.intValue(), value2.intValue());

        long max4 = Math.max(value1.longValue(), value2.longValue());
        long min4 = Math.min(value1.longValue(), value2.longValue());

        System.out.println("Max value in double: " + max1);
        System.out.println("Min value in double: " + min1);
        System.out.println("Max value in float : " + max2);
        System.out.println("Min value in float : " + min2);
        System.out.println("Max value in int   : " + max3);
        System.out.println("Min value in int   : " + min3);
        System.out.println("Max value in long  : " + max4);
        System.out.println("Min value in long  : " + min4);
    }
}

The result of the above program are:

Max value in double: 200.0
Min value in double: 100.0
Max value in float : 200.0
Min value in float : 100.0
Max value in int   : 200
Min value in int   : 100
Max value in long  : 200
Min value in long  : 100

How do I get the absolute value of a number?

By Wayan in Core API, Math 0 Comment

The example below show you how to get the absolute value of a number. To get the absolute value or the abs value of a number we use the Math.abs() method call. The Math.abs() method is an overloaded that can accept value in type of double, float, int or long.

package org.kodejava.math;

public class GetAbsoluteValueExample {
    public static void main(String[] args) {
        Double value = -10.0D;

        double abs1 = Math.abs(value);
        System.out.println("Absolute value in double: " + abs1);

        float abs2 = Math.abs(value.floatValue());
        System.out.println("Absolute value in float : " + abs2);

        int abs3 = Math.abs(value.intValue());
        System.out.println("Absolute value in int   : " + abs3);

        long abs4 = Math.abs(value.longValue());
        System.out.println("Absolute value in long  : " + abs4);
    }
}

The code snippet above print the following result:

Absolute value in double: 10.0
Absolute value in float : 10.0
Absolute value in int   : 10
Absolute value in long  : 10

How do I read data from a buffer into channel?

By Wayan in Core API, IO 0 Comment

In this example you’ll see how to read data from buffer using FileChannel.write() method call. Reading from a buffer means that you are writing data into the channel object. In the snippet below the data from our dummy buffer will be read and written into the result.txt file.

package org.kodejava.io;

import java.io.File;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class BufferRead {
    public static void main(String[] args) throws Exception {
        FileChannel channel = null;

        try {
            // Define an output file and create an instance of FileOutputStream
            File file = new File("result.txt");
            FileOutputStream fos = new FileOutputStream(file);

            // Create a dummy ByteBuffer which value to be read into a channel.
            ByteBuffer buffer = ByteBuffer.allocate(256);
            buffer.put(new byte[]{65, 66, 67, 68, 69, 70, 71, 72, 73, 74});

            // Change the buffer from writing mode to reading mode.
            buffer.flip();

            // Gets the channel from the FileOutputStream object and read the
            // data available in buffer using channel.write() method.
            channel = fos.getChannel();
            int bytesWritten = channel.write(buffer);
            System.out.println("written : " + bytesWritten);
        } finally {
            if (channel != null && channel.isOpen()) {
                channel.close();
            }
        }
    }
}