JSONObject.objectToBigDecimal precision errors when parsing doubles

[Bohlski]

When parsing doubles the method uses the BigDecimal(double) constructor, which can have unpredictable results as stated in the docs: https://docs.oracle.com/javase/7/docs/api/java/math/BigDecimal.html#BigDecimal(double)

It is instead preferred to use BigDecimal.valueOf(double)
https://docs.oracle.com/javase/7/docs/api/java/math/BigDecimal.html#valueOf(double)

This lead to a few precision errors on my end, when updating from an older version of this library.

[johnjaylward]

@Bohlski which version of the library is currently giving you the issue, the master branch or the latest release on Maven?

[Bohlski]

@johnjaylward The latest release on Maven

[johnjaylward]

Do you have a test case we can use to reproduce the issue?

…

On Wed, Jun 24, 2020, 03:38 Bohlski ***@***.***> wrote: @johnjaylward <https://github.com/johnjaylward> The latest release on Maven — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#531 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAC5VV7JNBEM5UBIRTKFQNDRYGUQLANCNFSM4OFN4OBA> .

[Bohlski]

Looks to me like any use of the constructor on a decimal will give the extra unwanted precision digits.
At least any time I've tried the results have been the same.

But I guess I can give a boiled down version of my current test:

public void testObjectToBigDecimal() {  
    double value = 1412078745.01074;  
    Reader reader = new StringReader("[{\"value\": " + value + "}]");
    JSONTokener tokener = new JSONTokener(reader);
    JSONArray array = new JSONArray(tokener);
    JSONObject jsonObject = array.getJSONObject(0);

    BigDecimal current = jsonObject.getBigDecimal("value");
    BigDecimal wantedValue = BigDecimal.valueOf(value);

    Assert.assertEquals(current, wantedValue);
 }

This fails with output
Expected :1412078745.01074
Actual :1412078745.0107400417327880859375

Within the newer versions (post version 20180813, I believe), getBigDecimal calls JSONObject.objectToBigDecimal which has the unwanted behaviour.

[stleary]

@Bohlski We will look into these questions:

• Have recent commits resulted in changed behavior, causing problems for lib users?
• When was the change introduced?
• Should the change be reverted?
• Should some other mitigation be provided?

[johnjaylward]

I used the test case provided and confirmed that the changes in latest master branch correct the issue.