The library Java entities define a minimal abstraction for calling Java from Logtalk. This abstraction makes use of Logtalk parametric objects and allows creating Java object, accessing Java class fields, and calling Java class and object methods using syntax closer to Logtalk. It also gives access to some Java utility predicates.
This abstraction was developed primarily to work with the JPL library bundled with SWI-Prolog and YAP. However, it’s expected to be implementable with alternative Java interfaces found in other backend Prolog compilers. Currently, a preliminary implementation is also available for JIProlog.
The main idea in this abstraction layer is to use parametric objects where the first parameter holds the Java reference (usually to a class or object) and an optional second parameter holds the return value. Together with a forward message handler, this allows the use of Java messages with the same functor and number of arguments as found in the relevant JavaDocs.
To load all entities in this library, load the
| ?- logtalk_load(java(loader)).
To test this library predicates, load the
| ?- logtalk_load(java(tester)).
The two main objects in this library are
java(Reference, ReturnValue) and
java(Reference). Use the latter
if you want to ignore the return value or when calling a void Java
java object implements utility predicates. For some backend Java
interfaces such as JPL (available in SWI-Prolog and YAP) there is also a
java_hook hook object for removing any overhead when using this
For usage examples and unit tests, see the
When running Java GUI examples on the macOS Terminal application, you may get a Java error saying that the AWT cannot be started. In alternative, try to run the example from within the SWI-Prolog macOS application instead of using the shell integration script. This issue is due to a macOS Java issue that’s orthogonal to both SWI-Prolog/YAP and Logtalk.