double is a Java primitive type.
A double variable may store a double-precision floating point value.
double ratio = .01; double diameter = 6.15; double height = 1.35E03; // 1.35 * 103 or 1350.0 double height = 1e-2; // 1.0 * 10-2 or 0.01
Since floating point data types are approximations of real numbers, you should generally never compare floating point numbers for equality.
Java floating point numbers can represent infinity and NaN (not a number). The Double wrapper class defines the constants MIN_VALUE, MAX_VALUE, NEGATIVE_INFINITY, POSITIVE_INFINITY and NaN.