java - Truncating float to the two first non-zero decimal digits -

i want truncate floating point numbers in java 2 first non-zero decimal digits. example, 0.000134 0.00013, or 11.00401 11.0040.

the solution can think of strip integral part, , multiply 10 until number bigger or equal 10. truncate original float number of multiplications decimal digits.

but might have operation often, i'm looking faster solution.

my test code:

public static string truncateto2nonzero(double f) {     int integral = (int)f;     double decimal = f - integral;     int digits = 0;      while (decimal < 10) {         decimal *= 10;         digits++;     }      double ret = (int)decimal / math.pow(10, digits);     ret += integral;      return double.tostring(ret); }  public static void main(string args[]) {     final int tests = 1000000;     double[] floats = new double[tests];      random random = new random();     (int = 0; < tests; ++i) {         int zeros = random.nextint(6) + 3; // divide 10^zeros         double digits = random.nextint(100) + 100; // 3 last digits         floats[i] = digits / math.pow(10,zeros) + random.nextint(20) + 1;     }      long starttime = system.nanotime();     (int = 0; < tests; ++i)         truncateto2nonzero(floats[i]);     long endtime = system.nanotime();      long duration = endtime - starttime;     system.out.println(duration / 1000000); // in milliseconds } 

i'm using windows 7 home premium 64-bit. output of java -version:

java version "1.8.0_20" java(tm) se runtime environment (build 1.8.0_20-b26) java hotspot(tm) 64-bit server vm (build 25.20-b23, mixed mode) 

when want "truncate" sounds display format. being said floats not friendly this. bigdecimals are. should give start, needs error checking of course.

static string roundtolasttwodecimaldigits(float f) {     // split whole number , decimals     string[] floatparts = new bigdecimal(f).toplainstring().split("\\.");      int wholenumberportion = integer.parseint(floatparts[0]);      // count zeroes     string decimalportion = floatparts[1];     int numdecimalplaces = 0;     while (decimalportion.charat(numdecimalplaces) == '0')         numdecimalplaces++;      // 3 digits round     string toround = decimalportion.substring(numdecimalplaces,             numdecimalplaces + 3);      int decimalforrounding = math.round(float.parsefloat(toround) / 10);      stringbuilder sb = new stringbuilder();      sb.append(wholenumberportion);     sb.append(".");     (int = 0; < numdecimalplaces; i++)         sb.append("0");     sb.append(decimalforrounding);      return sb.tostring(); }