Comment about JDK-8204458 - BigDecimal toString() return different value when use idea run and debug (original) (raw)
Jaikiran Pai jai.forums2013 at gmail.com
Wed Jun 20 05:13:50 UTC 2018
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(I don't have permissions to comment on the JIRA nor do I see a way to submit a comment, as a casual observer, to a bug opened by someone else through https://bugs.java.com/. So posting it here. I thought of sending it to "discuss" list instead of this one, but this felt more appropriate. I hope that's OK.)
As noted in the JIRA https://bugs.openjdk.java.net/browse/JDK-8204458 the following simple code:
public static void main(final String[] args) throws Exception { final BigDecimal bd = new BigDecimal("1"); System.out.println(bd.toString()); }
returns an "incorrect" output ("0") when run in debug mode with a breakpoint in IntelliJ IDE. Apparently not reproducible in other IDEs. I use IntelliJ, so gave it a quick try and indeed it does return "0" in a specific scenario. What actually triggers this and reproduces this, is the combination of 2 things:
- The breakpoint has to be in the constructor of the BigDecimal class (which is what the OP has done in that JIRA)
- The fact that the toString() implementation of this class uses a "stringCache"
What's really happening (in IntelliJ) is that when the IDE stops at that breakpoint, i.e. when the class instance isn't yet fully initialized, the IDE tries to render a IDE specific "Variables" view/window, where it displays the object instance details. To do so, it internally (in the background) appears to be triggering a toString() call on that instance being displayed. Effectively, what's happening is that the toString() implementation of this BigDecimal class goes and builds up a "stringCache" using an uninitialized/partially initialized state of this instance (which is still not finished in its constructor) and ends up storing an incorrect value of "0" to this "stringCache". As a result, the subsequent calls to toString(), even after the object is fully initialized return this incorrectly computed/cached value.
This appears to be something the IntelliJ team might have to handle better in their debug view/rendering, I guess. I see this as neither specific to BigDecimal nor as a bug in this implementation. I believe any similar class will run into similar problems for cases like these where the instance isn't yet fully initialized to be presented in the debug view.
-Jaikiran
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