PyJNIus

A Python module to access Java classes as Python classes using the Java Native Interface (JNI). Warning: the pypi name is now pyjnius instead of jnius.

Installation

pip install pyjnius

Quick overview

>>> from jnius import autoclass
>>> autoclass('java.lang.System').out.println('Hello world')
Hello world

>>> Stack = autoclass('java.util.Stack')
>>> stack = Stack()
>>> stack.push('hello')
>>> stack.push('world')
>>> print(stack.pop())
world
>>> print(stack.pop())
hello

Usage with python-for-android

• Get python-for-android
• Compile a distribution with kivy (PyJNIus will be automatically added)

Then, you can do this kind of things:

from time import sleep
from jnius import autoclass

Hardware = autoclass('org.renpy.android.Hardware')
print('DPI is', Hardware.getDPI())

Hardware.accelerometerEnable(True)
for x in xrange(20):
    print(Hardware.accelerometerReading())
    sleep(.1)

It will output something like:

I/python  ( 5983): Android kivy bootstrap done. __name__ is __main__
I/python  ( 5983): Run user program, change dir and execute main.py
I/python  ( 5983): DPI is 160
I/python  ( 5983): [0.0, 0.0, 0.0]
I/python  ( 5983): [-0.0095768067985773087, 9.3852710723876953, 2.2218191623687744]
I/python  ( 5983): [-0.0095768067985773087, 9.3948478698730469, 2.2218191623687744]
I/python  ( 5983): [-0.0095768067985773087, 9.3948478698730469, 2.2026655673980713]
I/python  ( 5983): [-0.028730420395731926, 9.4044246673583984, 2.2122423648834229]
I/python  ( 5983): [-0.019153613597154617, 9.3852710723876953, 2.2026655673980713]
I/python  ( 5983): [-0.028730420395731926, 9.3852710723876953, 2.2122423648834229]
I/python  ( 5983): [-0.0095768067985773087, 9.3852710723876953, 2.1835119724273682]
I/python  ( 5983): [-0.0095768067985773087, 9.3756942749023438, 2.1835119724273682]
I/python  ( 5983): [0.019153613597154617, 9.3948478698730469, 2.2122423648834229]
I/python  ( 5983): [0.038307227194309235, 9.3852710723876953, 2.2218191623687744]
I/python  ( 5983): [-0.028730420395731926, 9.3948478698730469, 2.2026655673980713]
I/python  ( 5983): [-0.028730420395731926, 9.3852710723876953, 2.2122423648834229]
I/python  ( 5983): [-0.038307227194309235, 9.3756942749023438, 2.2026655673980713]
I/python  ( 5983): [0.3926490843296051, 9.3086557388305664, 1.3311761617660522]
I/python  ( 5983): [-0.10534487664699554, 9.4331550598144531, 2.1068975925445557]
I/python  ( 5983): [0.26815059781074524, 9.3469638824462891, 2.3463177680969238]
I/python  ( 5983): [-0.1149216815829277, 9.3852710723876953, 2.31758713722229]
I/python  ( 5983): [-0.038307227194309235, 9.41400146484375, 1.8674772977828979]
I/python  ( 5983): [0.13407529890537262, 9.4235782623291016, 2.2026655673980713]

Advanced example

When you use autoclass, it will discover all the methods and fields of the class and resolve them. You may want to declare and use only what you need. The previous example can be done manually as follows:

from time import sleep
from jnius import MetaJavaClass, JavaClass, JavaMethod, JavaStaticMethod

class Hardware(JavaClass):
    __metaclass__ = MetaJavaClass
    __javaclass__ = 'org/renpy/android/Hardware'
    vibrate = JavaStaticMethod('(D)V')
    accelerometerEnable = JavaStaticMethod('(Z)V')
    accelerometerReading = JavaStaticMethod('()[F')
    getDPI = JavaStaticMethod('()I')

# use that new class!
print('DPI is', Hardware.getDPI())

Hardware.accelerometerEnable()
for x in xrange(20):
    print(Hardware.accelerometerReading())
    sleep(.1)

You can use the signatures method of JavaMethod and JavaMultipleMethod, to inspect the discovered signatures of a method of an object

>>> String = autoclass('java.lang.String')
>>> dir(String)
['CASE_INSENSITIVE_ORDER', '__class__', '__cls_storage', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__javaclass__', '__javaconstructor__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__pyx_vtable__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'charAt', 'checkBounds', 'clone', 'codePointAt', 'codePointBefore', 'codePointCount', 'compareTo', 'compareToIgnoreCase', 'concat', 'contains', 'contentEquals', 'copyValueOf', 'empty', 'endsWith', 'equals', 'equalsIgnoreCase', 'finalize', 'format', 'getBytes', 'getChars', 'getClass', 'hashCode', 'indexOf', 'indexOfSupplementary', 'intern', 'isEmpty', 'join', 'lastIndexOf', 'lastIndexOfSupplementary', 'length', 'matches', 'nonSyncContentEquals', 'notify', 'notifyAll', 'offsetByCodePoints', 'regionMatches', 'registerNatives', 'replace', 'replaceAll', 'replaceFirst', 'split', 'startsWith', 'subSequence', 'substring', 'toCharArray', 'toLowerCase', 'toString', 'toUpperCase', 'trim', 'valueOf', 'wait']
>>> String.format.signatures()
[(['java/util/Locale', 'java/lang/String', 'java/lang/Object...'], 'java/lang/String'), (['java/lang/String', 'java/lang/Object...'], 'java/lang/String')]

Each pair contains the list of accepted arguments types, and the returned type.

Troubleshooting

Make sure a Java Development Kit (JDK) is installed on your operating system if you want to use PyJNIus on desktop. OpenJDK is known to work, and the Oracle Java JDK should work as well.

On windows, make sure JAVA_HOME points to your java installation, so PyJNIus can locate the jvm.dll file allowing it to start java. This shouldn't be necessary on OSX and Linux, but in case PyJNIus fails to find it, setting JAVA_HOME should help.

Support

If you need assistance, you can ask for help on our mailing list:

• User Group : https://groups.google.com/group/kivy-users
• Email : kivy-users@googlegroups.com

We also have a Discord server:

https://chat.kivy.org/

Contributing

We love pull requests and discussing novel ideas. Check out our contribution guide and feel free to improve PyJNIus.

The following mailing list and IRC channel are used exclusively for discussions about developing the Kivy framework and its sister projects:

• Dev Group : https://groups.google.com/group/kivy-dev
• Email : kivy-dev@googlegroups.com

License

PyJNIus is released under the terms of the MIT License. Please refer to the LICENSE file for more information.

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