Dynamically Editing/creating Classes In Java Android

I am looking for a way to dynamically define classes and instantiate them in Android, at runtime. From my understanding, this is already done in Android, I just need some help fig

Solution 1:

Don't do this :)

I actually doubt there are JSON libraries that behave this way; the two accepted ways I know (I am not an expert on this, though) are either to create some sort of data structure holding name-value pairs - i.e. add stuff to a data structure but not create a new class - or prepare a template of a class which will be populated from a JSON object.

Java, being statically-typed, is not really suitable for creating whole new classes at run-time, and there is no reflection support for that - though there is support for accessing objects of unknown types (e.g. querying for all their fields / methods).

What you can do is to manually write a java class to a file - either in Java code and then compile it somehow, or directly in bytecode - and then load that file at runtime. It's ugly, but it will work. Then it's just the same as any runtime loading of classes - either you rely on the base class / interface of the loaded class, or you have to use reflection to do anything meaningful with it.

Solution 2:

For those who really do want to do this (for instance using Dalvik's JIT to create a fast interpreter for another language), there is this project:

http://code.google.com/p/dexmaker/

Which allows you to programatically create classes, variables and methods.

Solution 3:

Generating Dalvik Bytecode at Runtime on-device Using ASM or BCEL

This example use ASM and BCEL to generete two classes on-device. The classes are created into SD Card memory and then they are loaded into Android operating system dynamically.

The following class is the template of the example:

public class HelloWorld {
    public static void hello(){
        int a=0xabcd;
        int b=0xaaaa;
        int c=a-b;
        String s=Integer.toHexString(c);
        System.out.println(s);
    }

}

Firstly I have used BCEL or ASM to create a new ad-hoc class in SD Card. Secondly I have converted the Java Class to a Dex Class with the Dxclient utiliy in SD Card. Finally I have created a jar file and then I have loaded this package into the device from SD Card

DXClient reference

https://github.com/headius/dexclient/blob/master/src/DexClient.java