Just Java™ 2

Limited Accuracy of Floating Point Types

Before we describe double and float, we need to point out two limitations of floating-point arithmetic. People are still getting Ph.D.s for probing the mathematics underlying floats, but the short story is:

• Floating-point numbers only hold a limited number of significant figures. The float type only holds six to seven significant figures. So you can hold the number 123,456 accurately, and you can hold the number 0.123456 pretty accurately, but it's certain that you cannot hold the number 123,456.123456 in a float variable accurately because that would require 12 significant figures. You can write the number in your program, and you'll actually get a number that is approximately the value you want, ...