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Calculating Logarithms in Java

Calculating Logarithms in Java

1. Introduction

In this short tutorial, we’ll learn how to calculate logarithms in Java. We’ll cover both common and natural logarithms as well as logarithms with a custom base.

2. Logarithms

A logarithm is a mathematical formula representing the power to which we must raise a fixed number (the base) to produce a given number.

In its simplest form, it answers the question: How many times do we multiply one number to get another number?

We can define logarithm by the following equation:

3. Calculating Common Logarithms

Logarithms of base 10 are called common logarithms.

To calculate a common logarithm in Java we can simply use the Math.log10() method:

public void givenLog10_shouldReturnValidResults() {
    assertEquals(Math.log10(100), 2);
    assertEquals(Math.log10(1000), 3);

4. Calculating Natural Logarithms

Logarithms of the base e are called natural logarithms.

To calculate a natural logarithm in Java we use the Math.log() method:

public void givenLog10_shouldReturnValidResults() {
    assertEquals(Math.log(Math.E), 1);
    assertEquals(Math.log(10), 2.30258);

5. Calculating Logarithms With Custom Base

To calculate a logarithm with custom base in Java, we use the following identity:

public void givenCustomLog_shouldReturnValidResults() {
    assertEquals(customLog(2, 256), 8);
    assertEquals(customLog(10, 100), 2);

private static double customLog(double base, double logNumber) {
    return Math.log(logNumber) / Math.log(base);

6. Conclusion

In this tutorial, we’ve learned how to calculate logarithms in Java. As always all source code is available on GitHub.

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