JPype for Android

We ported JPype to the Android system. There are a number of important differences between JPype on Android and on a JVM. The Andoid platform uses the Dalvik virtual machine(DVM) which supports only a portion of the Java specification. As a result some portions of JPype have been removed or function differently.

Supported Functions

The following features operate the same on both the JVM and DVM version.

  • Java classes using jpype.JClass

  • Access to Java methods and fields

  • Java arrays using jpype.JArray including slicing and direct transfers

  • Java primitive types, string type, and boxed types

  • Java.nio byte buffer including memory mapped data

  • Python collections API for Java collection types

  • Class customizers and type conversions

  • Support of scientific codes such as numpy

  • Implementation of Java interfaces using JProxy

Functional differences

When using JPype on Android, the virtual machine is started prior to the start of Python. Thus, there is no need to lauch the machine. Instead to use jpype only the statement import jpype is required. In addtion, the following functions have been removed…

  • jpype.startJVM is removed as the virtual machine cannot be started more than once.

  • jpype.shutdownJVM is removed as DVM cannot to stopped during operation.

  • jpype.addClassPath is removed as DVM does not support class path based jar loading. Dex files can be loaded dynamically using the Android API.

  • jpype.getDefaultJVMPath is removed as there is no JVM on Android.

  • jpype.beans has been removed as adding addition properties for semantic sugar increase the memory profile unnecessarily.

  • attach and detaching of threads is not allowed and those entry points have been removed.

Removed JPype Services

Not all JPype services are provided on Android as some functions depend on the internals of the JVM. These include…

  • The dynamic class loader does not operate on JPype as DVM does not support jar files.

  • jpype.imports and jpype.JPackage use the jar file system to identify packages which is not available on DVM. Therefore, all classes must be loaded use jpype.JClass.

  • jpype support for Javadoc was removed as DVM does not support Javadoc jars in the classpath.

  • jpype does not install interrupt handlers for ^C on Android.

Unsupported Java libraries

Some Java libraries are not supported on Android.

  • Bytecode manipulation libraries to not function on DVM. This means generation of dynamic classes, manipulation of loaded classes, and Java agent code will not function.

  • Some standard Java libraries are not implemented on Android such as AWT. Jar libraries that access these unimplemented libraries will not function.

  • Private JVM internal classes such as sun.* are not implemented and cannot be used.

Behavior differences

Some changes in JPype behavior occur simply because the DVM operates differently. These changes include

  • java.lang.Class.forName will not load classes from classes.dex. Attempting to access classes with forName will get ClassNotFoundException. Applying forName to base classes that use the system classloader function as expected.