Floating point arithmetic not producing exact results
floating-point, java
Solution
If you need exact decimal values, you should use `java.math.BigDecimal`. Then read "What Every Computer Scientist Should Know About Floating-Point Arithmetic" for the background of why you're getting those results.
(I have a .NET-centric article which you may find easier to read - and certainly shorter. The differences between Java and .NET are mostly irrelevant for the purposes of understanding this issue.)
Problem
I need to do some floating point arithmetic in Java as shown in the code below: ``` public class TestMain { private static Map<Integer, Double> ccc = new HashMap<Integer, Double>() { { put(1, 0.01); put(2, 0.02); put(3, 0.05); put(4, 0.1); put(6, 0.2); put(10, 0.5); put(20, 1.0); put(30, 2.0); put(50, 5.0); put(100, 10.0); } }; Double increment(Double i, boolean up) { Double inc = null; while (inc == null) { inc = ccc.get(i.intValue()); if (up) --i; else ++i; } return inc; } public static void main(String[] args) { TestMain tt = new TestMain(); for (double i = 1; i < 1000; i += tt.increment(i, true)) { System.out.print(i + ","); } } } ``` This is to simulate the range of values given as output by the Betfair spinner widget. Floating point arithmetic in Java seems to introduce some unexpected errors. For example, I get 2.180000000000001 instead of 2.18. What use are floating point numbers is you can't trust the results of arithmetic performed on them? How can I get around this issue?