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Im new to app development and was wondering if it would be possible to include another jdk. For example java 17 and run a jar that needs to be run in this exact version? I think termux has an api that you may use for these purposes but is there another possibility? These jars are only console based and without any gui.

I first tried to use the jar as a android library inside the app, which did not work since it was compiled in java version 17. I tried decompiling the jar and recompiling it with the version I was using. The problem is that all the libraries used are on other versions than I need them to be and so I could not recompile it. I also thought about writing the application in c# but I am not used to it at all, which would throw many new problems that I would be willing to take if it would be a possibility to work out my project.

Packesl
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1 Answers1

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Q: Is loading the code into your Android application an option?

A: No.

  • Android loads code from ".dex" files not ".class" files.
  • The ".class" files would need to be translated using dx.
  • The Android dx command doesn't understand Java 17 ".class" file format.
  • Also the code in the JAR is likely to depend on classes in the Java SE class library that the Android doesn't provide.

Q: What about running it in a separate Android VM?

A: No.

  • An Android VM requires ".dex" files; see above.
  • Also, the Java SE class library issue; see above.

Q: What about launching an OpenJDK or Oracle Java 17 JVM on the Android device to run the JAR?

A: In theory Yes, but in practice No. As far as I am aware, there is no port of OpenJDK Java SE to the Android OS platform.

Q: What about using Termux?

A: OK ... that might work. See Is it possible to install the JDK on an android device?.

I have no experience with this, and don't know what problems you may run into doing this. But I suspect that you wouldn't be able to distribute something that relies on Termux via the Google Playstore.

Another option is to download the source code1 for the application and try to build it in your Android dev environment

  • If the code uses Java classes / packages / libraries that are not available for Android, recode the relevant parts of the application to use Android equivalents instead.
  • Ditto if the code uses Java language features that are not yet supported in Android Java.
  • It probably won't be easy. It may turn out to be impractical.

1 - You said in a comment that the code your are trying to use is "open source". So the "download source and build it" option is available to you. I'm puzzled why you tried to decompile and recompile it instead ...

Stephen C
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  • Q: Is loading the code into your Android application an option? What about loading it in as a library? Like this: https://stackoverflow.com/questions/25660166/how-to-add-a-jar-in-external-libraries-in-android-studio. Wouldn't that be possible for jars? – Packesl Jan 08 '23 at 13:31
  • I'm not planning to upload it to the Google play store it doesn't have to meet all their restrictions. It's just for me to learn while also having projects that make me have lots of fun – Packesl Jan 08 '23 at 13:35
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    Code is code ... whether it is a "library" or an "application". JAR files contain code ... and the code is the issue. If you want to load code in / into an Android JVM, it needs to be in the form of ".dex" files ... in your JAR file or whatever. See above. – Stephen C Jan 08 '23 at 14:15