Java - Math.log() method example

The Math.log() method returns the natural logarithm (base e) of a number. 

public class MathExample {

    public static void main(String[] args) {
        // Natural logarithm (logarithm with base e):
        //                            x            y
        System.out.println( Math.log( 1    ) ); // 0
        System.out.println( Math.log( 7    ) ); // 1.9459101490553132
        System.out.println( Math.log( 10   ) ); // 2.3025850929940460
        System.out.println( Math.log( 100  ) ); // 4.6051701859880920
        System.out.println( Math.log( 1000 ) ); // 6.9077552789821370

        System.out.println( Math.log( -1        ) ); //  NaN
        System.out.println( Math.log(  0        ) ); // -Infinity
        System.out.println( Math.log( Double.POSITIVE_INFINITY ) ); // +Infinity

        System.out.println( Math.E ); // 2.718281828459045

        // Logarithm with custom base is placed in below example.
    }
}

The Math.log() method is presented on the following chart:

1. Documentation

package java.lang;

public final class Math {

    public static double log(double x) { ... }

}

2. Logarithm with custom base example

This example shows a logarithmic function calculation with its own base.

public class MathExample {
    
    static double calculateLogarithm(double base, double x) {
        double a = Math.log(x);
        double b = Math.log(base);

        return a / b;
    }

    public static void main(String[] args) {
        // Logarithm with custom base:
        //                                    base      x               y
        System.out.println( calculateLogarithm( 2,      2      ) ); //  1.0
        System.out.println( calculateLogarithm( 2,      4      ) ); //  2.0
        System.out.println( calculateLogarithm( Math.E, Math.E ) ); //  1.0
        System.out.println( calculateLogarithm( 3,      9      ) ); //  2.0
        System.out.println( calculateLogarithm( 3,      81     ) ); //  4.0
        System.out.println( calculateLogarithm( 10,     10     ) ); //  1.0
    }
}

References

1. Natural logarithm - Wikipedia