Question

I have a set of numbers with varying precision. I need to create a hashkey out of them.
This code shows that the numbers are equal (at the relevant precision). So, what is a hash function that returns equal value for equal numbers?

    int prec = 2;
    double val=12.3456;
    int digits = (int)Math.log(val);
    MathContext mc = new MathContext(digits+prec);
    BigDecimal bd = new BigDecimal(12.3020, mc);
    System.out.println("Value A:"+bd.toString());

    MathContext mcx = new MathContext(digits+prec-1);
    BigDecimal bdx = new BigDecimal(12.3170, mcx);
    System.out.println("Value A:"+bdx.toString());

    System.out.println("Difference is:"+bdx.compareTo(bd));
    System.out.println("HashCode A:"+bd.hashCode());
    System.out.println("HashCode B:"+bdx.hashCode());

BTW, BigDecimal didn’t work out of the box for me, because 12.34 @ 2 precision was 12 … I need the precision to effect everything past the decimal point. (So, is there a more appropriate library class for this?)

Answer 1

One answer that seems to work is:

new Double(bd.doubleValue()).hashCode()

Let me know if this is somehow wrong.