How do I calculate cube root and square root of a number?

By Wayan in Core API, Math 0 Comment

To calculate the cube root and the square root of a double value we can use the Math.cbrt(double a) and Math.sqrt(double a) static method call.

package org.kodejava.math;

public class CubeSquareRootExample {

    public static void main(String[] args) {
        double cube = 125.0d;
        double square = 100.0d;

        // Get the cube root of double value
        double cubeRoot = Math.cbrt(cube);
        System.out.println("Cube root of " + cube + " is " + cubeRoot);

        // Get the square root of double value
        double squareRoot = Math.sqrt(square);
        System.out.println("Square root of " + square + " is " + squareRoot);
    }
}

This snippet will print the following output:

Cube root of 125.0 is 5.0
Square root of 100.0 is 10.0

How do I reread the content of a buffer?

By Wayan in Core API, IO 0 Comment

The example shown below tells you how to reread the contents of a buffer. To reread the data from a buffer we can use the buffer’s rewind() method. This method set the position back to 0 while the limit is unchanged, it still holds the value of how many data can be read from the buffer.

package org.kodejava.io;

import java.nio.CharBuffer;

public class BufferRewind {
    public static void main(String[] args) {
        CharBuffer buffer = CharBuffer.allocate(1024);
        buffer.put("The quick brown fox jumps over the lazy dog.");
        buffer.flip();

        // Read buffer's data using the get() method call.
        while (buffer.hasRemaining()) {
            System.out.print(buffer.get());
        }
        System.out.println();

        // Rewind the buffer will set the position back to 0.
        // We rewind the buffer so that we can reread the buffer
        // data for another purposes.
        buffer.rewind();

        // Reread the buffer and append its data to a StringBuilder
        StringBuilder bufferText = new StringBuilder();
        while (buffer.hasRemaining()) {
            bufferText.append(buffer.get());
        }
        System.out.println(bufferText);
    }
}

The output of the code snippet:

The quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog.

How do I use trigonometric calculation methods?

By Wayan in Core API, Math 0 Comment

This example demonstrates how to use the trigonometric methods of the java.lang.Math class. You can see the use of method such as Math.sin(), Math.cos(), Math.tan(), etc.

package org.kodejava.math;

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

        double sine = Math.sin(radians);
        double cosine = Math.cos(radians);
        double tan = Math.tan(radians);

        double asine = Math.asin(sine);
        double acosine = Math.acos(cosine);
        double atan = Math.atan(tan);

        System.out.println("Sine of " + radians + " = " + sine);
        System.out.println("Cosine of " + radians + " = " + cosine);
        System.out.println("Tangent of " + radians + " = " + tan);
        System.out.println("Arcsine of " + sine + " = " + asine);
        System.out.println("Arccosine of " + cosine + " = " + acosine);
        System.out.println("Arctangent of " + tan + " = " + atan);
    }
}

The output of the program are:

Sine of 1.0 = 0.8414709848078965
Cosine of 1.0 = 0.5403023058681398
Tangent of 1.0 = 1.5574077246549023
Arcsine of 0.8414709848078965 = 1.0
Arccosine of 0.5403023058681398 = 1.0
Arctangent of 1.5574077246549023 = 1.0

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();
            }
        }
    }
}

How do I change the buffer mode between write and read?

By Wayan in Core API, IO 0 Comment

A buffer can be read or written. To change the mode between the write mode and read mode we use the flip() method call on the buffer.

There are few things that you should know when you change between the write mode to the read mode. A buffer have the capacity, position and limit properties. The capacity will always be the same on write or read mode. But the position and limit will store different information in each mode.

In write mode the limit will be equals to the capacity, but in read mode the limit will be equals to the last position where the last data were written. The position on the write mode point where the data will be written in the buffer. When calling the flip() method the position will be set to 0 and the limit will be set to the last value of the position.

package org.kodejava.io;

import java.nio.CharBuffer;

public class BufferFlip {
    public static void main(String[] args) {
        CharBuffer buffer = CharBuffer.allocate(1024);
        System.out.println("capacity = " + buffer.capacity());
        System.out.println("position = " + buffer.position());
        System.out.println("limit    = " + buffer.limit());

        buffer.put("Java NIO Programming");

        System.out.println("capacity = " + buffer.capacity());
        System.out.println("position = " + buffer.position());
        System.out.println("limit    = " + buffer.limit());

        buffer.flip();
        System.out.println("capacity = " + buffer.capacity());
        System.out.println("position = " + buffer.position());
        System.out.println("limit    = " + buffer.limit());
    }
}

The program will print the following result:

capacity = 1024
position = 0
limit    = 1024
capacity = 1024
position = 20
limit    = 1024
capacity = 1024
position = 0
limit    = 20

How do I write data into ByteBuffer using put method?

By Wayan in Core API, IO 0 Comment

The snippet below show you how to write some bytes into the java.nio.ByteBuffer object through a call to the put() method.

package org.kodejava.io;

import java.nio.ByteBuffer;

public class BufferPut {
    public static void main(String[] args) {
        ByteBuffer buffer = ByteBuffer.allocate(32);
        buffer.put((byte) 65);
        buffer.put((byte) 66);
        buffer.put((byte) 67);
        buffer.put((byte) 68);
        buffer.put((byte) 69);


        // Writes a sequence of bytes
        byte[] bytes = new byte[]{70, 71, 72, 73, 74};
        buffer.put(bytes);

        // Write to the beginning of the buffer
        buffer.put(0, (byte) 75);

        buffer.flip();

        while (buffer.hasRemaining()) {
            System.out.print((char) buffer.get());
        }
    }
}