How to run CONSOLE Java code on Android

>Download and install Termux (best app)
>Open and run the command apt update && apt upgrade && pkg upgrade
This command is very important! You should run it whenever you want to use the Advanced Package Tool or pkg
>Now make sure you have ecj, dx, and dalvikvm by individually running ecj --version, dx --version, dalvikvm --version
>>If you don't have it, it should say 'The program '[tool]' is not installed. Install it by executing:
pkg install [tool]' or '...apt-get install [tool]'
pkg is a newer tool used; I had to use apt-get since I had this app for a long time.
Use whatever it tells you to use

>I recommend going to your home folder cd ~ and making a directory called Java mkdir Java and cd in there cd Java and make project folders inside /Java
>In there [project folder], make a Java code using nano or vim editor. I use vim.
>Compile your code with ecj File1.java File2.java or, if first compilation, use ecj *.java
Don't always use *.java unless necessary; slows down compilation time by compiling already good code again
>You should now get .class files. Check with ls *.class
>Compile them to Dalvik bytecode so that Android can read it using dx --dex --output=MainClass.dex *.class
The output must have the extension dex
>Finally, run it by dalvikvm -cp MainClass.dex MainClass
-cp means classpath so you must specify the class which has the main entry point. No extension