How to not lose decimal places when doing "longProperty1.divide(longProperty2)"?

Question

I have two LongProperty (there are no decimal places in a long) variables (longProperty1 and longProperty2). I need to divide them and I need to keep the division result in a DoubleProperty (there are decimal places in a double) variable (result) without losing decimal places.

final DoubleProperty result = new SimpleDoubleProperty(0.0);
final LongProperty longProperty1 = new SimpleLongProperty(45);
final LongProperty longProperty2 = new SimpleLongProperty(7);
result.bind(longProperty1.divide(longProperty2));
System.out.println(result.get()); //print: "6.0" instead of "6.428571428571429" (lost decimal places)

longProperty1 and longProperty2 are of type LongProperty because they receive very large numbers, so I can't cast them to DoubleProperties.

On the other hand, the result will receive a value from 0.0 to 1.0 (for example: 0.0, 0.2975, 0.5378, 0.9853, 1.0), because in my real problem longProperty1 <= longProperty2(for example: 500/600=0.8333, 1/2=0.5, 1897/5975=0.3174, ...).

How to do this?

Answer 1

The methods provided LongProperty (and by other NumberExpressions) such as divide are convenience methods. You can create a custom binding that does whatever you want:

final DoubleProperty result = new SimpleDoubleProperty(0.0);
final LongProperty longProperty1 = new SimpleLongProperty(812323534);
final LongProperty longProperty2 = new SimpleLongProperty(956745323);
result.bind(Bindings.createDoubleBinding(() -> longProperty1.longValue() / (double) longProperty2.longValue(),
    longProperty1, longProperty2));
System.out.println(result.get());
longProperty1.set(612323534);
System.out.println(result.get());

Bindings is a utility class for creating bindings. Here I created a custom binding that returns a double by casting the division of longs to double. You will lose precision here.

The output of the above is:

0.8490488685670847
0.6400068223798362

Answer 2

You should use BigDecimal for your calculations.
LongProperty is just a wrapper for usual long value, so no decimal points.

You can try doing longProperty1.divide(longProperty2.doubleValue()) as well, which would call DoubleBinding divide(final double other), but I think this would remove the point of using LongProperty.