Can't set UNNECESSARY roundingMode about gwt HOT 3 CLOSED

I'm not understanding what you expect to happen here - when I run either line from a normal JVM (i.e. not GWT), I get an exception (tested in Java 11 and 21, line numbers below from 11):

Exception java.lang.ArithmeticException: Rounding necessary
      at BigDecimal.commonNeedIncrement (BigDecimal.java:4653)
      at BigDecimal.needIncrement (BigDecimal.java:4860)
      at BigDecimal.divideAndRound (BigDecimal.java:4835)
      at BigDecimal.setScale (BigDecimal.java:2923)
      at BigDecimal.setScale (BigDecimal.java:2838)

Are you sure that this should work as you have it written? Or are you saying that GWT incorrectly does not throw an exception here (though GWT's behavior appears to the same at a brief glance...)?

from gwt.

Well that's how Java has defined BigDecimal. If you want to reduce the scale you have to tell BigDecimal how to round the number in order to fit into the new scale.

Reducing the scale using RoundingMode.UNNECESSARY can only be successful if your BigDecimal has enough zeros at the end. If you want to truncate your BigDecimal to a given scale you should use RoundingMode.DOWN/FLOOR.

Also in your example you have used the constructor BigDecimal(double) which is kind of a beast as there are many double values that cannot be represented exactly in binary form. Given your example number 91.0202 one might think the scale is 4 but in reality it is 46 because 91.0202 cannot be represented exactly. The binary form of that number represents 91.0202000000000026602720026858150959014892578125.

So it is advisable to use the constructor BigDecimal(String) instead.

Using the string based constructor something like below will work:

new BigDecimal("92.0200").setScale(2, RoundingMode.UNNECESSARY);
new BigDecimal("92.0200").setScale(2);

It works because the number has two zeros at the end and thus fits into a scale of 2 without any rounding.

from gwt.

Closing the issue because the exception is expected based on the provided example.

from gwt.