Show me the code! – By Davanum Srinivas

December 4, 2007

Command line Java on DalvikVM

Filed under: Uncategorized — Davanum Srinivas @ 11:21 am

Found this very useful when i was trying out the JNI under android (Short Story – Could not get it to work!).

Step #1: Start with a simple java class

package org.apache;

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

Compile the java class

C:\android\CmdLine>javac -d . -g Helloworld.java

Step #2: Package the generated classes into a temporary jar

C:\android\CmdLine>jar -cvf Temp.jar *
added manifest
adding: Hello.java(in = 0) (out= 0)(stored 0%)
adding: HelloWorld.java(in = 149) (out= 122)(deflated 18%)
adding: org/(in = 0) (out= 0)(stored 0%)
adding: org/apache/(in = 0) (out= 0)(stored 0%)
adding: org/apache/HelloWorld.class(in = 556) (out= 344)(deflated 38%)

Step #3: Use the “dx” tool to generate a classes.dex from our temporary jar.

C:\android\CmdLine>dx --dex --output=c:/android/CmdLine/classes.dex c:/android/CmdLine/Temp.jar

Step #4: Use the “aapt” tool to create a new jar suitable for use with dalvikvm

C:\android\CmdLine>aapt add CmdLine.jar classes.dex
 'classes.dex'...

and push it into a known location on the emulator

C:\android\CmdLine>adb push CmdLine.jar /data
30 KB/s (0 bytes in 481.000s)

Step #5: kick the tires of dalvikvm

C:\android\CmdLine>adb shell
# /system/bin/dalvikvm -Xbootclasspath:/system/framework/core.jar -version
/system/bin/dalvikvm -Xbootclasspath:/system/framework/core.jar -version
DalvikVM version 0.2.0
Copyright (C) 2007 Google, Inc.
Blah blah blah LICENSE blah blah.
Dalvik VM init failed (check log file)

Step #6: Run our code

# /system/bin/dalvikvm -Xbootclasspath:/system/framework/core.jar -classpath /data/CmdLine.jar org.apache.HelloWorld
/system/bin/dalvikvm -Xbootclasspath:/system/framework/core.jar -classpath /data/CmdLine.jar org.apache.HelloWorld
Hello World!
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5 Comments »

  1. Good example and clear instructions, but it doesn’t run if you try to instantiate the class in the main function to do advanced stuff (like have a finalize clause). An error occurs when I attempted to do this:

    Dalvik VM unable to find static main(String[]) …

    Using Android 1.6.

    Comment by Ryan Page — November 20, 2009 @ 12:28 pm

  2. This doesnt make J2ME jars to be run on android is it?
    only simple java jars run on this dalvik java

    Comment by sparco — February 23, 2010 @ 2:19 am

  3. What would be the additional steps needed if the HelloWorld program needs to refer to external classes/packages?

    Comment by Stephen — May 24, 2011 @ 10:48 am

  4. I’m having severe problems with my mobile and being redirected to other web sights..

    Comment by David Burgess — March 27, 2012 @ 2:08 am

  5. Two additional points that were needed for me:
    1) Run dalvikvm as root, otherwise you don’t have permission to write to /data/dalvikvm-cache
    $ su -
    2) add the required LD_LIBRARY_PATH for dalvikvm:
    # export LD_LIBRARY_PATH=/system/lib
    3) run the vm
    # /system/bin/dalvikvm -Xbootclasspath:/system/framework/core.jar -classpath /data/CmdLine.jar org.apache.HelloWorld

    To discover this:
    $ logcat *:S dalvikvm:D

    1)
    8<————————————————————————
    E/dalvikvm( 3400): Dex cache directory isn't writable: /data/dalvik-cache
    I/dalvikvm( 3400): Unable to open or create cache for Hello2.jar (/data/dalvik-cache/storage@sdcard0@tmp@Hello2.jar@classes.dex)
    8<————————————————————————

    2)
    8<————————————————————————
    D/dalvikvm( 4927): Trying to load lib libjavacore.so 0×0
    D/dalvikvm( 4927): Added shared lib libjavacore.so 0×0
    D/dalvikvm( 4927): Trying to load lib libnativehelper.so 0×0
    D/dalvikvm( 4927): Added shared lib libnativehelper.so 0×0
    W/dalvikvm( 4927): Exception Ljava/lang/NullPointerException; thrown while initializing Ljava/lang/System;
    8<————————————————————————

    Comment by vanrenter — December 8, 2013 @ 8:39 am


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