What is special about this math? [duplicate]

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Java floating point arithmetic

What is special about this double math in Java? I would expect the answer of .9 - 1 to be -0.1, however the response is -0.09999999999999998

double a = 0.9;
double b = 1.0;
double c = a - b;
System.out.println(c);
>>-0.09999999999999998

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Floating point precision is difficult for computers. See this article and Retain precision with double in Java for details

For accurate floating point arithmetic use BigDecimal

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Yet another question about precision of doubles. Doubles have limited precision. Not all numbers can be represented precisely!

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The value 0.9 cannot be represented exactly in binary form.

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double is not exact. this is the nearest number that can be represented by double.

try to read what every programmer should know about floating point arithmetic.

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There are an infinite number of numbers between any two values.

There are a finite number of memory bits on any computer. So any way we chose to represent floating point numbers will never be exact.