When browsing the Spring's source code, I encountered code like if (!Boolean.FALSE.equals(pv.conversionNecessary)) {...}
After some research, I also found codes like !Boolean.FALSE.equals and !Boolean.TRUE.equals exist in other open-source projects too.
I wonder what's the possible reasons for not using the apparently concise expression?
There are various reasons why this kind of thing might be necessary.
In this example, pv is an instance of PropertyValue which declares the conversionNecessary as follows:
/** Package-visible field that indicates whether conversion is necessary. */
@Nullable
volatile Boolean conversionNecessary;
From this, we can infer that it is not unexpected for conversionNecessary to be null.
So ... the verbose form if (!Boolean.FALSE.equals(pv.conversionNecessary)) {...} is dealing with the null case. Boolean.FALSE.equals(null) is false.
By contrast, the more concise form if (!pv.conversionNecessary) {...} would throw an NPE.
It is also worth noting that since conversionNecessary is volatile here, an alternative version that did an explicit null check would need to use a temporary variable to avoid race conditions; e.g.
Boolean necessary = pv.conversionNecessary;
if (necessary == null || necessary) { ... }
Another scenario where you might do this kind of thing is if the declared type of the variable is Object rather than Boolean.