Question

I have a program called MyProgram.java. I want to run it from different directory which will be run on another machine. So I made a directory and copied MyProgram.class file and made a .bat file that runs it (Run.bat) which includes the command: @java MyProgram.

This didn’t work, I had to copy SPVerification$1.class that was generated from Eclipse in order to make it work.

What is this XXX$1.class files and why do I need them beside the XXX.class file in order to run an application?

Answer 1

They are anonymous inner classes. In other words, when you have a piece like

class OuterClass {
    // ...
    void method() {
        Thread t = new Thread(new Runnable() { 
            // ... code implementing Runnable interface ... 
        });
        // ... code to use t or whatever
    }
}

That generates anonymous inner class, in this case implementing the Runnable interface, and compiled code of that class goes to a OuterClass$<number>.class file. You can have more than one such class, with increasing number in the .class file name.

Note that syntax is exactly the same even if you extend a class with the anonymous inner class, instead of implementing an interface. This is a slightly different from creating named classes, where you need to use implements and extends as appropriate.