The circumference of a circle is 2πr where r is the radius.

The area of a circle is πr² where r is the radius.

A complete circle is 2 π radians. One radian is about 57.2957795 degrees, measured counterclockwise from due east. Java’s Math. sin and Math.cos etc. work in radians.

There are two convenience methods for interconverting degress and radians.

// built-in radians <-> degrees methods.
public static double toDegrees ( double angleInRadians );
public static double toRadians ( double angleInDegrees );