Java 8 DecimalFormat gives inconsistent output

Question

JDK 8

DecimalFormat x = new DecimalFormat("0.000");
System.out.println(x.format(4.4804));
System.out.println(x.format(4.4805));
System.out.println(x.format(4.5805));
System.out.println(x.format(4.5804));

Output

I am aware about the JDK7 bug. But even in JDK 8 it is not consistent. am I doing something wrong?

Print `new BigDecimal(4.5805).toString()` and `new BigDecimal(4.4805).toString()` to see there is no bug here and this is behaving exactly like described in the linked question. — Tunaki, Aug 10 '16 at 11:40

score 4 · Accepted Answer · edited Aug 10 '16 at 15:42

As suggested by the comment to the question, your observed results are caused by your numeric literals being interpreted as double values which may not be represented exactly, e.g.,

System.out.println(new BigDecimal(4.4805).toString());

produces

4.48050000000000014921397450962103903293609619140625

which is then rounded to 4.481 because it is just past the half-way point between 4.480 and 4.481. You will see more consistent results if you tweak your code sample to

DecimalFormat x = new DecimalFormat("0.000");
System.out.println(x.format(new BigDecimal("4.4804")));
System.out.println(x.format(new BigDecimal("4.4805")));
System.out.println(x.format(new BigDecimal("4.5805")));
System.out.println(x.format(new BigDecimal("4.5804")));

Java 8 DecimalFormat gives inconsistent output

1 Answers1