Working with string representations of floating-point values can produce incorrect conclusions about the precision of the values. For example, consider the conversion of a value from type float to type double, a widening primitive conversion. Refer to the guideline "NUM17-J. Beware of precision loss when converting primitive integers to floating-point" for more details about such conversions.
String representations of floating-point numbers shall not be compared or inspected. When the value of a float variable must be represented exactly using the double type, an explicit assignment is more appropriate than first converting the floating-point value to a String and then to a double.
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int i = 1;
String s = Double.valueOf(i / 1000.0).toString();
if (s.equals("0.001")) {
// ...
}
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However s actually contain contains the string "0.0010". Consequently, the comparison unexpectedly fails.
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int i = 1;
String s = Double.valueOf(i / 1000.0).toString();
s = s.replaceFirst("[.0]*$", "");
if (s.equals("0.001")) {
// ...
}
|
Thie While the comparison does succeed on this the code .However, the comparison above, it fails on this the similar code below, which uses 1/10000.0 instead of 1/1000.0. The string produced is not 0.00010 but rather 1.0E-4.
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Relying on the string representation of floating-point types can result in imprecise values.
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Related Vulnerabilities
Bibliography
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NUM13-J. Do not construct BigDecimal objects from floating-point literals 03. Numeric Types and Operations (NUM) NUM15-J. Ensure conversions of numeric types to narrower types do not result in lost or misinterpreted data