"java import" in script

Ignition
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I'm a python3 programmer. I see a lot of "from java.XXX import XXX". I wonder is it a standard function in jython, or only ingition? Where should I start, is there a manual or guide?
Before this, I used to use python libraries for everything.

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Standard function in jython. With some quirks:

  • Wildcard imports are not supported for java packages.

  • Jython automatically "wraps" java objects with a dynamic subclass of PyObject, creating matching methods and fields. When such a wrapped object is handed to a true java method that doesn't take a PyObject, but does take the inner java type, the wrapper is automatically stripped back off.

  • Python native types are marshalled into similar java types. SImilar in reverse for java primitive types. Jython has a central system for managing and customizing this marshalling and unmarshalling process. See this related topic:

  • java's getXyz() and setXyz(val) are automatically mapped to jython property xyz via jython's internal java machinery that implements @property. So both the original java methods and a python-style property become available on such "NetBeans" objects. Using the property is fewer opcodes for the jython interpreter, so should be used wherever applicable.
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Thanks reply.

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Generally speaking in Ignition, you should prefer a Java-centric approach over a Python one. The environment is the JVM, so Java libraries (including the standard library) are better maintained and supported than Jython. If you need a third party library or SDK for something, you'll also usually have a much better time getting the Java code to work in Ignition than a Python library.

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I suppose this topic is the best place to add some detail to the bullet points describing jython's java support.

  • Jython's wrapping operation is built around the java class object, which becomes a jython type object. In jython, a type object is how you get to a constructor, so java's class objects can be treated the same way. (There's no new keyword, so this is how you instantiate java in jython.)

  • Jython's wrapping/marshalling/unmarshalling code does a bunch of caching for performance, so once a java class's wrapper is computed, the overhead is very low.

  • Jython doesn't fully accommodate java's overloaded method signatures. It approximates it by differentiating by the number of function arguments, not by the argument types. If this ambiguity causes the wrong method to be called for a specific case, your only option is to use java reflection to extract exactly the method you need, and call it indirectly.

  • The NetBeans-style automatic property <=> method connection mechanism only works when the short property name doesn't clash with a method name or public field name. Those are created for the type wrapper first, and NetBeans properties cannot replace them. Keep in mind that JavaDocs are for java programmers, not jython programmers, and do not reflect jython's efforts to be helpful in this way.

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