CollectionsIntegration

Background

Currently, the support for Java Collections integration is a one-way street. It's possible to make Collections object act as a PyObject but it's not possible to make a PyObject act as a Collection.

The integration of Collections into Jython happens through the CollectionProxy and CollectionProxy2 classes. They wrap the Collection instance with the appropriate proxy and delegate Jython calls to the Collection instance.

Going the other way fails. Take for example:

•     >>> from java.util import ArrayList
      >>> a = ArrayList([1,2,3])
      Traceback (innermost last):
        File "<console>", line 1, in ?
      TypeError: java.util.ArrayList(): 1st arg can't be coerced to java.util.Collection or int

In this example the ArrayList constructor is expecting a java.util.Collection instance but since the PyList does not implement this interface the TypeError is thrown. Since the Collection framework is fundamental to Java since 1.2 the JythonDevelopmentTeam will address this issue. The work is currently being managed by ClarkUpdike.

Design

There are two different approaches:

1. Subclass the Abstract classes available in java.util for the Collection framework.

2. Continuing subclassing PyObject with the additional work of implementing the appropriate interface.

Approach 2 offers the best integration options. Jython is primarily an implementation of Python so implementing the data structures as they are in Python takes priority over the Java implementations. In addition, the keyword and index arguments for method calls are already done. The implementation of the interfaces will need only delegate to the appropriate PyObject instance's method for the same functionality.