How to compare two double values in Java?

Question

A simple comparison of two double values in Java creates some problems. Let's consider the following simple code snippet in Java.

package doublecomparision;  final public class DoubleComparision  {     public static void main(String[] args)      {         double a = 1.000001;         double b = 0.000001;          System.out.println("\n"+((a-b)==1.0));     } } 

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The above code appears to return true, the evaluation of the expression ((a-b)==1.0) but it doesn't. It returns false instead because the evaluation of this expression is 0.9999999999999999 which was actually expected to be 1.0 which is not equal to 1.0 hence, the condition evaluates to boolean false. What is the best and suggested way to overcome such a situation?

Answer 1

Basically you shouldn't do exact comparisons, you should do something like this:

double a = 1.000001; double b = 0.000001; double c = a-b; if (Math.abs(c-1.0) <= 0.000001) {...} 

Answer 2

Instead of using doubles for decimal arithemetic, please use java.math.BigDecimal. It would produce the expected results.

For reference take a look at this stackoverflow question