Floating-Point Types in Java

Floating-Point Types

Floating-point numbers, also known as real numbers, are used when evaluating expressions
that require fractional precision. For example, calculations such as square root, or transcendentals
such as sine and cosine, result in a value whose precision requires a floating-point type. Java
implements the standard (IEEE–754) set of floating-point types and operators. There are two
kinds of floating-point types, float and double, which represent single- and double-precision
numbers, respectively. Their width and ranges are shown here:

NameWidth in bitsApproximate Range
double644.9e–324 to 1.8e+308
float321.4e–045 to 3.4e+038

The type float specifies a single-precision value that uses 32 bits of storage. Single precision isfaster on some processors and takes half as much space as double precision, but will become imprecise when the values are either very large or very small. Variables of type float are useful when you need a fractional component, but don’t require a large degree of precision. For example, float can be useful when representing dollars and cents.
Here are some example float variable declarations:
float hightemp, lowtemp;

Double precision, as denoted by the double keyword, uses 64 bits to store a value. Double precision is actually faster than single precision on some modern processors that have been optimized for high-speed mathematical calculations. All transcendental math functions, such as sin( ), cos( ), and sqrt( ), return double values. When you need to maintain accuracy over many iterative calculations, or are manipulating large-valued numbers, double is the best
Here is a short program that uses double variables to compute the area of a circle:

// Compute the area of a circle.
class Area {
public static void main(String args[]) {
double pi, r, a;

r = 10.8; // radius of circle
pi = 3.1416; // pi, approximately
a = pi * r * r; // compute area

System.out.println("Area of circle is " + a);