NUM11-J. Do not compare or inspect the string representation of floating-point values

String representations of floating-point numbers should not be compared or inspected. If they are used, significant care needs to be taken to ensure expected behavior.

Noncompliant Code Example (String Comparison)

This noncompliant code example incorrectly compares the decimal string literal generated by 1/10000.0 . The string produced is not 0.0001 but rather 1.0E-4 .

int i = 1;
String s = Double.valueOf(i / 10000.0).toString();
if (s.equals("0.0001")) {
  // ...
}

Compliant Solution (String Comparison)

This compliant solution uses the BigDecimal class to avoid the conversion into scientific notation. It then performs a numeric comparison, which passes as expected.

int i = 1;
BigDecimal d = new BigDecimal(Double.valueOf(i / 10000.0).toString());
if (d.compareTo(new BigDecimal("0.0001")) == 0) {
  // ...
}

Risk Assessment

Comparing or inspecting the string representation of floating-point values may have unexpected results.

Automated Detection

Android Implementation Details

Comparing or inspecting the string representation of floating-point values may have unexpected results on Android.

Bibliography

[ API 2006 ]
[ JLS 2015 ]
[ Seacord 2015 ]	NUM11-J. Do not compare or inspect the string representation of floating-point values LiveLesson