Programming in Java bytecode [closed]

Question

I'm looking to write a short program (maybe a Hello World) in Java bytecode. I just want to write the bytecode using my text editor and run it. How would I do this? Got an example? Thanks!

Answer 1

You could try Jasmin!

.class public HelloWorld .super java/lang/Object  .method public static main([Ljava/lang/String;)V   .limit stack 3   .limit locals 1    getstatic      java/lang/System/out Ljava/io/PrintStream;   ldc            "Hello World."   invokevirtual  java/io/PrintStream/println(Ljava/lang/String;)V    return  .end method 

You compile it using:

 > java -jar jasmin.jar hello.j 

And then you run it like any class:

 > java HelloWorld Hello World. 

Update

I see that your question mentions "without using Javac or Java". Could you clarify how you meant that statement?

Answer 2

I've created a new Java bytecode assembler that is backwards compatible with Jasmin but also adds lots of new features and simplifies the syntax slightly.

Here's an example of how you might write a Hello World program.

.class public hello .super java/lang/Object  .method public static main : ([Ljava/lang/String;)V     .limit stack 10     .limit locals 10      getstatic java/lang/System out Ljava/io/PrintStream;     ldc "Hello World!"     invokevirtual java/io/PrintStream println (Ljava/lang/Object;)V     return .end method 

I've also written a tutorial on bytecode assembly. It currently only covers Hello, World, but I can continue it if there is interest.