Page History

Because floating-point numbers can represent fractions, programmers often mistakenly assume that they can represent any simple fraction exactly. In fact, floating-point numbers are subject to precision range limitations just as integers are. FurtherFurthermore, limited-precision binary floating-point numbers cannot represent all decimal fractions exactlydecimals precisely, even when the fractions decimals can be represented in a small number of decimal digits.

In addition, because floating-point numbers can represent large values, programmers often mistakenly assume that they can represent all digits of those values. To gain a large dynamic range, floating-point numbers maintain a fixed number of bits of precision and an exponent. Incrementing a large floating-point value might not change that value within the available precision.

Consequently, floating-point variables should must not be used as loop counters.

...

This noncompliant code example uses a floating-point variable as a loop counter. The decimal number 0.1 is a repeating fraction in binary and cannot be exactly represented as a binary floating-point numbercan not be precisely represented as a float or even as a double.

for (float x = 0.1f; x <= 1.0f; x += 0.1f) {
  // System... out.println(x);
}

This loop executes only nine times. (If the value of x is printed inside the loop, the following values appear: , and produces the following output:

0.1

...

0.2

...

0.3

...

0.4

...

0.5

...

0.6

...

0.70000005

...

0.8000001

...

0.9000001

...

Compliant Solution

This compliant solution uses an integer loop counter from which the desired floating-point value is derived.

for (int count = 1; count <= 10; count += 1) {
  float x = count/10.0f;
  // System.out..println(x);
}

Noncompliant Code Example

...