sum - How to avoid floating point precision errors with floats or doubles in Java?

Question

I have a very annoying problem with long sums of floats or doubles in Java. Basically the idea is that if I execute:

for ( float value = 0.0f; value < 1.0f; value += 0.1f )
    System.out.println( value );

What I get is:

0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.70000005
0.8000001
0.9000001

I understand that there is an accumulation of the floating precision error, however, how to get rid of this? I tried using doubles to half the error, but the result is still the same.

Any ideas?

Answer 1

There is a no exact representation of 0.1 as a float or double. Because of this representation error the results are slightly different from what you expected.

A couple of approaches you can use:

• When using the double type, only display as many digits as you need. When checking for equality allow for a small tolerance either way.
• Alternatively use a type that allows you to store the numbers you are trying to represent exactly, for example BigDecimal can represent 0.1 exactly.

Example code for BigDecimal:

BigDecimal step = new BigDecimal("0.1");
for (BigDecimal value = BigDecimal.ZERO;
     value.compareTo(BigDecimal.ONE) < 0;
     value = value.add(step)) {
    System.out.println(value);
}

See it online: ideone