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Bug Cor 46

Inspired by

Original Description

This code checks to see if a floating point value is equal to the special Not A Number value (e.g., if (x == Double.NaN)). However, because of the special semantics of NaN, no value is equal to NaN, including NaN. Thus, x == Double.NaN always evaluates to false. To check to see if a value contained in x is the special Not A Number value, use Double.isNaN(x) (or Float.isNaN(x) if x is floating point precision). – 2013-10-15

Detailed Description

When working with floating point variables (such as Float and Double) one often wants to test if an invalid operation has been invoked. To this end one should use the Float.isNaN(f) function and do NOT test equality to the public constant NaN defined in the Float or Double class. As a matter of fact, no variable will ever be equal to the NaN constant, due to its special semantics.

NaN is just a variable defined in many programming languages to give a “meaningful” result to operations that otherwise have no mathematically defined result. The value NaN (Not a number) results from the following operations:

  • Complex values
    • √x where x is negative
    • log(x) where x is negative
    • tan(x) where x mod 180 is 90
    • asin(x) or acos(x) where x is outside [-1..1]
  • 0/0
  • ∞/∞
  • ∞/−∞
  • −∞/∞
  • −∞/−∞
  • 0×∞
  • 0×−∞
  • 1∞
  • ∞ + (−∞)
  • (−∞) + ∞

Sample Problem Scenario

<code Java> Float f; if (f == Float.NaN){

System.out.println("IS NAN");

}

Double d; if (d == Double.NaN){

System.out.println("IS NAN");

} </Code>

Sample Counter Scenario

Sample Fix

<code Java>

Float f; if (Float.isNaN(f)){

System.out.println("IS NAN");

}

Double d; if (Double.isNaN()){

System.out.println("IS NAN");

} </Code>

Evaluation Results

Benchmark project Time # Hits Precision Recall
FB JT FB JT Delta FB JT Delta
Apache Tomcat < 1s00 100% 100% 0 100% 100% 0
Argo UML < 1s00 100% 100% 0 100% 100% 0
AWT < 1s00 100% 100% 0 100% 100% 0
Jakarta < 1s00 100% 100% 0 100% 100% 0
Java IO < 1s00 100% 100% 0 100% 100% 0
JHotDraw < 1s00 100% 100% 0 100% 100% 0
jrefactory < 1s00 100% 100% 0 100% 100% 0
JServlet < 1s00 100% 100% 0 100% 100% 0
JUnit < 1s00 100% 100% 0 100% 100% 0
Lexi < 1s00 100% 100% 0 100% 100% 0
Mapper XML < 1s00 100% 100% 0 100% 100% 0
nutch < 1s00 100% 100% 0 100% 100% 0
PMD < 1s00 100% 100% 0 100% 100% 0
quickuml < 1s00 100% 100% 0 100% 100% 0

FB = FindBugs, JT = JTransformer, Delta = JTransformer - FindBug

All measurements were taken on a machine with the following properties:

  • JT Version: 4.0.0
  • Eclipse Kepler
  • Windows 8.1
  • i5 2,30Ghz
  • 8 GB Main Memory
  • SSD Hardrive
teaching/labs/mdse/2013/bug_descriptions/jt-bug-cor46.txt · Last modified: 2018/05/09 01:59 (external edit)

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