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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!

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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?

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9 Comments

This post makes me want to fake the work I'm doing today and tinker around with Jasmin. :-)
+1 Jasmin is what came to my mind and I couldn't remember the name. It was featured in a book that explains JVM internals. I Forget the name of the book too, sigh...
@Bakkal: According to the link: "Jasmin was originally created as a companion to the book "Java Virtual Machine", written by Jon Meyer and Troy Downing and published by O'Reilly Associates."
by "without using Javac or Java," I just meant that I want to write the code using bytecode. Thanks for the info!
wow~ This is super cool. is this JVM independent as well? can this run on a blackberry jvm?
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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.

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the link is broken
Sorry about that. It looks like the whole wiki is gone. I'll email them to see if they can bring it back or have any copies.
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Byte code is written as actual bytes, which are not normally easily editable by a normal text editor.

This means you will need something that converts a textual representation to binary. A reasonable place to start would be an assembler like Jasmin.

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