Hello, I mentioned a while ago the idea of moving a utility that I find quite useful from commons-geometry to commons-text, which would be a more appropriate home for it. There was not any interest at the time but I've made a few improvements to the class and I'd like to try again. The utility in question is the DoubleFormats [1] class. This class contains factory methods for producing lightweight, thread-safe DoubleFunction<String> instances for converting doubles to decimal strings in different formats. The class is specifically designed for data output; no localization is performed. It is used in commons-geometry to provide a way to control the precision and formatting of double values in text-based geometric data formats such as OBJ. I've found that although the JDK provides a number of different ways to format doubles (eg, String.format, DecimalFormat, BigDecimal, etc), none of them have fit the requirements for performant, thread-safe data output. Hence, the reason for this class.
Below are examples of each of the types of formats available and some outputs. The arguments passed to each method are the precision (maximum number of non-zero decimal digits) and min exponent (base 10 exponent for the smallest non-zero number that should be represented). // plain decimal representation; no scientific format DoubleFunction<String> plain = DoubleFormats.createPlain(5, -3); plain.apply(1); // 1.0 plain.apply(1e10); // 10000000000.0 plain.apply(1234.567); // 1234.6 plain.apply(0.00356); // 0.004 // scientific format DoubleFunction<String> sci = DoubleFormats.createScientific(5, -3); sci.apply(1); // 1.0 sci.apply(1e10); // 1.0E10 sci.apply(1234.567); // 1.2346E3 sci.apply(0.00356); // 4.0E-3 // engineering format DoubleFunction<String> eng = DoubleFormats.createEngineering(5, -3); eng.apply(1); // 1.0 eng.apply(1e10); // 10.0E9 eng.apply(1234.567); // 1.2346E3 eng.apply(0.00356); // 4.0E-3 // default format; uses the Double.toString() convention of representing // numbers less that 10^-3 or greater than 10^7 using scientific format and // other numbers using plain decimal format DoubleFunction<String> def = DoubleFormats.createDefault(5, -3); def.apply(1); // 1.0 def.apply(1e10); // 1.0E10 def.apply(1234.567); // 1234.6 def.apply(0.00356); // 0.004 The performance of all of these methods is comparable to DecimalFormat or BigDecimal. The benchmark output below shows the results of formatting 10000 double values using standard Double.toString(), a simple BigDecimal conversion, DecimalFormat (single instance), and a function returned from DoubleFormats.createDefault(). Double.toString() is the clear winner but the rest are all quite close. Benchmark (size) Mode Cnt Score Error Units DoubleFormatsPerformance.doubleToString 10000 avgt 5 3837610.399 ± 62668.705 ns/op DoubleFormatsPerformance.bigDecimal 10000 avgt 5 6279807.365 ± 93566.619 ns/op DoubleFormatsPerformance.decimalFormat 10000 avgt 5 5787717.633 ± 168626.950 ns/op DoubleFormatsPerformance.doubleFormatsDefault 10000 avgt 5 5779534.166 ± 69496.434 ns/op Please let me know if there is any interest in moving this class to commons-text. It's primary advantages are that it is -thread-safe (unlike DecimalFormat), -performant (unlike String.format()), and -allows a variety of output formats (unlike BigDecimal). I would also be open to discussion and improvements on the design/implementation. Regards, Matt J [1] https://github.com/apache/commons-geometry/blob/master/commons-geometry-io-core/src/main/java/org/apache/commons/geometry/io/core/utils/DoubleFormats.java
