Java - Math.PI property example

The Math.PI property returns π number (3.141592653589793...).

public class MathExample {

    public static void main(String[] args) {

        // ------------------------------------------------------
        // Math.PI value priting:

        System.out.println( Math.PI ); // 3.141592653589793

        // ------------------------------------------------------
        // Math.PI with circle:

        final double radius = 5;

        // 1. Circle surface area:
        double area = Math.PI * Math.pow(radius, 2);
        System.out.println( area ); // 78.53981633974483

        // 2. Circle circumference:
        double circumference = 2 * Math.PI * radius;
        System.out.println( circumference ); // 31.41592653589793
    }
}

1. Documentation

package java.lang;

public final class Math {

    public static final double PI = 3.14159265358979323846;

}

2. Nilakantha series example

To calculate PI number Nilakantha series can be used.

public class CustomMath {

    static double computePi(int iterations) {
        double approximation = 3;
        double a = 2;
        for (int i = 0; i < iterations; i++) {
            approximation += 4 / (a * (++a) * (++a));
            approximation -= 4 / (a * (++a) * (++a));
        }
        return approximation;
    }

    public static void main(String[] args) {

        System.out.println( CustomMath.computePi(    1 ));  // 3.1333333333333333
        System.out.println( CustomMath.computePi(    2 ));  // 3.1396825396825396
        System.out.println( CustomMath.computePi(    5 ));  // 3.1414067184965018
        System.out.println( CustomMath.computePi(   10 ));  // 3.141565734658547
        System.out.println( CustomMath.computePi(   20 ));  // 3.141589028940776
        System.out.println( CustomMath.computePi(   50 ));  // 3.1415924109719824
        System.out.println( CustomMath.computePi(  100 ));  // 3.141592622804848
        System.out.println( CustomMath.computePi(  200 ));  // 3.1415926497127264
        System.out.println( CustomMath.computePi(  500 ));  // 3.141592653340544
        System.out.println( CustomMath.computePi( 1000 ));  // 3.141592653558594
        System.out.println( CustomMath.computePi( 2000 ));  // 3.141592653585895
        System.out.println( CustomMath.computePi( 5000 ));  // 3.141592653589538
    }
}

References

1. Pi - Wikipedia