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

$ javac HelloWorld.java
$ jar -cvf HelloWorld.jar HelloWorld.class
$ d8 --output hw.jar HelloWorld.jar
$ adb push hw.jar /data/local/tmp

$ export CLASSPATH=/data/local/tmp/hw.jar
$ app_process /data/local/tmp HelloWorld
Hello World!