How do I raised a number to the power of n?

By I Wayan Saryada in Core API, Math 1 Comment

The static method Math.pow(double a, double b) can be used to raise the value specified in the a, the first argument, (the base), to the power of the value specified in b, the second argument, (the exponent). The exponent tells us how many times the base should be multiplied by itself. So, if I have the number of 5, and I want to raise it to the 3rd power, it means that I have to multiply 5 by itself for 3 times.

There are some special cases for the Math.pow() method, as you can read in the Javadocs, here four of them taken from the Javadocs:

  • If the second argument is positive or negative zero, then the result is 1.0.
  • If the second argument is 1.0, then the result is the same as the first argument.
  • If the second argument is NaN, then the result is NaN.
  • If the first argument is NaN and the second argument is nonzero, then the result is NaN.

You can read more detail about the Math.pow() method on the following Javadocs, Math.pow().

Let’s see a code snippet as an example:

package org.kodejava.math;

public class PowerExample {

    public static void main(String[] args) {
        double cubeRoot = 5d;

        // Get the cubed number of cube root
        // x cubed = x^3 (multiplication three times)
        double cubed = Math.pow(cubeRoot, 3);
        System.out.println(cubeRoot + " cubed is " + cubed);

        // Raised to zero
        System.out.println("Math.pow(2, 0): " + Math.pow(2, 0));

        // Raised to one
        System.out.println("Math.pow(2, 1): " + Math.pow(2, 1));

        // Raised to NaN
        System.out.println("Math.pow(2, Double.NaN): " + Math.pow(2, Double.NaN));

        // NaN raised to the nonzero exponent
        System.out.println("Math.pow(Double.NaN, 2): " + Math.pow(Double.NaN, 2));
    }
}

Our program print the following output:

5.0 cubed is 125.0
Math.pow(2, 0): 1.0
Math.pow(2, 1): 2.0
Math.pow(2, Double.NaN): NaN
Math.pow(Double.NaN, 2): NaN

How do I calculate logarithm?

By I Wayan Saryada in Core API, Math 0 Comment

We can calculate logarithm using the Math.log10() and the Math.log() static method call.

package org.kodejava.math;

public class LogarithmExample {

    public static void main(String[] args) {
        double number1 = 1000.0d;

        // Get common logarithm
        double log10 = Math.log10(number1);
        System.out.println("Common logarithm of " + number1 + " = " + log10);

        // Get natural logarithm
        double loge = Math.log(number1);
        System.out.println("Natural logarithm of " + number1 + " = " + loge);
    }
}

The output of the program is:

Common logarithm of 1000.0 = 3.0
Natural logarithm of 1000.0 = 6.907755278982137

How do I round a number?

By I Wayan Saryada in Core API, Math 0 Comment

The example below show you some methods of the Math class that can be used to round the value of a number. These methods are Math.ceil(), Math.floor() and Math.round().

package org.kodejava.math;

public class GetRoundedValueExample {

    public static void main(String[] args) {
        Double number = 1.5D;

        // Get the smallest value that is greater than or equal to the
        // argument and is equal to a mathematical integer
        double roundUp = Math.ceil(number);
        System.out.println("Result of rounding up of " + number + " = " + roundUp);

        // Get the largest value that is less than or equal to the
        // argument and is equal to a mathematical integer
        double roundDown = Math.floor(number);
        System.out.println("Result of rounding down of " + number + " = " + roundDown);

        // Get the closest long value to the argument
        long round1 = Math.round(number);
        System.out.println("Rounding result of " + number + " (in long) = " + round1);

        // Get the closest int value to the argument
        int round2 = Math.round(number.floatValue());
        System.out.println("Rounding result of " + number + " (in int) = " + round2);
    }
}

Here are the result of the program:

Result of rounding up of 1.5 = 2.0
Result of rounding down of 1.5 = 1.0
Rounding result of 1.5 (in long) = 2
Rounding result of 1.5 (in int) = 2

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

By I Wayan Saryada 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 I Wayan Saryada 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.