When shall use float type in Java?

Question

I know float type is A IEEE floating point, and it's not accuracy in calculation, for example, if I'd like to sum two floats 8.4 and 2.4, what I get is 10.7999999 rather than 10.8. I also know BigDecimal can solve this problem, but BigDecimal is much slower than float type.

In most real productions we'd like an accuracy value like above 10.8 not a 10.7999.. so my question is shall I prevent to use float as much as I can in programming? if not is there any use cases? I mean in a real production.

Answer 1

If you're handling monetary amounts, then numbers like 8.4 and 2.4 are exact values, and you'll want to use BigDecimal for those. However, if you're doing a physics calculation where you're dealing with measurements, the values 8.4 and 2.4 aren't going to be exact anyway, since measurements aren't exact. That's a use case where using double is better. Also, a scientific calculation could involve things like square roots, trigonometric functions, logarithms, etc., and those can be done only using IEEE floats. Calculations involving money don't normally involve those kinds of functions.

By the way, there's very little reason to ever use the float type; stick with double.

Answer 2

You use float when the percision is enough. It is generally faster to do calculations with float and requires less memory. Sometimes you just need the performance.

Answer 3

What you describe is caused by the fact that binary floating point numbers cannot exactly represent many numbers that can be exactly represented by decimal floating point numbers, like 8.4 or 2.4.

This affects not only the float type in Java but also double.

In many cases you can do calculations with integers and then rescale to get the deciamls correctly. But if you require numbers with equal relative accurracies, no matter how large they are, floating point is far superior.

So yes, if you can, you should prefer integers over floats, but there are many applications where floating point is required. This includes many scientific and mathematical algorithms.

You should also consider that 10.7999999 instead of 10.8 looks weird when displayed but actually the difference is really small. So it's not so much an accurracy issue but more related to number formatting. In most cases this problem is resolved by rounding the number appropriately when converting it to a string for output, for example:

String price = String.format("%.2f", floatPrice);

Answer 4

BigDecimals are very precise (you can determine their precision -- it is mainly limited by memory) but pretty slow and memory intensive. You use them when you need exact results, i.e. in financial applications, or when you otherwise need very precise results and when speed is not too critical.

Floating point types (double and float) are not nearly as precise, but much faster and they only take up limited memory. Typically, a float takes up 4 bytes and a double takes up 8 bytes. You use them with measurements that can't be very exact anyway, but also if you need the speed or the memory. I use them for (real time) graphics and real time music. Or when otherwise precision of the result is not so important, e.g. when measuring time or percentages when downloading or some such.