On Wed, Dec 4, 2024 at 3:47 PM Eirik Bjørsnøs <eir...@gmail.com> wrote:
> The OpenJDK includes many boolean flags in the form of system properties.
> These toggle different behavior such as debug logging, verification,
> caching, compatibility and conditional features.
>
To learn more about how the JDK uses boolean system properties, I conducted
a survey of the ones I could identify in java.base and thought it could be
useful to share the observations:
First, some definitions:
a) A *boolean system property *(BSP) is one whose value is evaluated to
either true or false.
b) A BSP *defaults* to either true or false*.*The default value is used
when a system property has no configured value.
c) A system property is either *case sensitive* or *case insensitive*. A
case insensitive property ignores the case when comparing configured values
with "true or "false".
d) The *normalized value* of a BSP is one of TRUE, FALSE, EMPTY or OTHER.
e) The normalized value is evaluated to true or false using a *definition
of truth*. This is the set of normalized values which are considered as
true.
Theoretically, there are 14 possible definitions of truth (sets of size
1-3). However, given that we want TRUE and FALSE be stable, there are not
many practical ones, and in fact, the JDK uses only three:
isTrue: {TRUE}
isTrueOrEmpty: {TRUE, EMPTY}
isNotFalse: {TRUE, EMPTY, OTHER}
Additionally, there is the "isSet" definition which considers any set value
as true, including "false".
*Some stats:*
Total number of BSPs found in java.base: 83
*Default values:*
Default false: 66
Default true: 17
*Case sensitivity:*
Case sensitive: 5
Case insensitive: 76
*Definitions of truth:*
isTrue: 61
isTrueOrEmpty: 15
isNotFalse: 5
isSet: 2
*Positive or negative name:*
Additionally, I looked into whether a system property name has a positive
or negative name. Names such as "allow" or "enable" are considered
positive, while names like "disable" or "inhibit" are considered negative:
Positive: 65
Negative: 8
Hope this was useful!
Thanks,
Eirik.
