can't edit class file with recaf.0.9 without re-compile

Question

I have this java code

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

I compile to class file, run it , and all fine.

I want to edit it via class file.

I open the HelloWorld.class with recaf.0.9, click on recompile, than I edit the code and save it, but the code not changes.

How can I edit .class file and not recompile it , and not working with bytecode.

I want for example add if else to this code(via the class file)

Answer 1

How can I edit .class file and not recompile it , and not working with bytecode.

These requirements are contradictory. You have to choose one or the other.

There are two main ways to edit Java code. You can either decompile the classfile, edit the decompiled source, and then try to compile it again, or you can edit it directly at the bytecode level using a bytecode disassembler and assembler such as Krakatau or a bytecode editor such as Recaf.

Decompilation and recompilation is unreliable, since the process is lossy in both directions, so it will generally only work in simple cases. You're better off editing the bytecode directly, since this is faster and guaranteed to work for all classfiles, but it does require you to understand bytecode. Note that Recaf is also lossy (unlike Krakatau), although it won't matter unless you're doing something highly unusual.