Determine Number of Decimal Place using BigDecimal

Question

I was interested to have the following getNumberOfDecimalPlace function:

System.out.println("0 = " + Utils.getNumberOfDecimalPlace(0));          // 0
System.out.println("1.0 = " + Utils.getNumberOfDecimalPlace(1.0));      // 0
System.out.println("1.01 = " + Utils.getNumberOfDecimalPlace(1.01));    // 2
System.out.println("1.012 = " + Utils.getNumberOfDecimalPlace(1.012));  // 3
System.out.println("0.01 = " + Utils.getNumberOfDecimalPlace(0.01));    // 2
System.out.println("0.012 = " + Utils.getNumberOfDecimalPlace(0.012));  // 3

May I know how can I implement getNumberOfDecimalPlace, by using BigDecimal?

The following code doesn't work as expected:

public static int getNumberOfDecimalPlace(double value) {
    final BigDecimal bigDecimal = new BigDecimal("" + value);
    final String s = bigDecimal.toPlainString();
    System.out.println(s);
    final int index = s.indexOf('.');
    if (index < 0) {
        return 0;
    }
    return s.length() - 1 - index;
}

The following get printed :

0.0
0 = 1
1.0
1.0 = 1
1.01
1.01 = 2
1.012
1.012 = 3
0.01
0.01 = 2
0.012
0.012 = 3

However, for case 0, 1.0, it doesn't work well. I expect, "0" as result. But they turned out to be "0.0" and "1.0". This will return "1" as result.

Answer 1

Combining Turismo, Robert and user1777653's answers, we've got:

int getNumberOfDecimalPlaces(BigDecimal bigDecimal) {     return Math.max(0, bigDecimal.stripTrailingZeros().scale()); } 

• stripTrailingZeros() ensures that trailing zeros are not counted (e.g. 1.0 has 0 decimal places).
• scale() is more efficient than String.indexOf().
• A negative scale() represents zero decimal places.

There you have it, the best of both worlds.

Answer 2

This code:

int getNumberOfDecimalPlaces(BigDecimal bigDecimal) {     String string = bigDecimal.stripTrailingZeros().toPlainString();     int index = string.indexOf(".");     return index < 0 ? 0 : string.length() - index - 1; } 

... passes these tests:

assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.001")), equalTo(3)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.01")), equalTo(2)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("0.1")), equalTo(1)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.000")), equalTo(0)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.00")), equalTo(0)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("1.0")), equalTo(0)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("1")), equalTo(0)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("10")), equalTo(0)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.1")), equalTo(1)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.01")), equalTo(2)); assertThat(getNumberOfDecimalPlaces(new BigDecimal("10.001")), equalTo(3)); 

... if that is indeed what you want. The other replies are correct, you have to use BigDecimal all the way through for this rather than double/float.

Answer 3

Without having to convert to String, it should be more efficient to use the scale directly:

  private int getNumberOfDecimalPlaces(BigDecimal bigDecimal)
  {
    int scale =  bigDecimal.stripTrailingZeros().scale();
    return scale>0?scale:0;
  }

Answer 4

That should do it

int getNumberOfDecimalPlace(BigDecimal number) {
    int scale = number.stripTrailingZeros().scale();
    return scale > 0 ? scale : 0;
}