Question

I am trying to round down a double using Big decimal and then comparing to another number For example:

    // Parse the string to extract the double and then put it into Big
    // decimal
    BigDecimal bdAns = BigDecimal.valueOf(Double.parseDouble("3.1419"));
    System.out.println(bdAns);
    BigDecimal bdCorr = BigDecimal.valueOf(Double.parseDouble("3.142"));
    System.out.println(bdCorr);
    System.out.println(bdCorr.precision() + " , " + bdAns.precision());
    // Round down the value of the bdAns, so that the precision of bdAns and
    // bdCorr matches. This code doesnt seem to work.
    bdAns = BigDecimal.valueOf(bdAns).setScale(bdCorr.precision(),
            BigDecimal.ROUND_UNNECESSARY);
    System.out.println(bdAns);
    System.out.println(bdAns.compareTo(bdCorr));

The last println is printing -1.But they should be equal as 3.1419 round to 3 places after decimal should be 3.142. Can somebody please tell me what is wrong with the code?

Answer 1

precision and scale are not the same thing, it appears you are confusing the two. scale is the number of digits to the right of the decimal point. precision is the total number of digits.

Change all of your references to precision to scale and it should work (but you’ll have to pick a rounding mode other than UNNECESSARY).