Any risk using a single dollar sign `$` as a java class name?

Question

Originally I was using the underscore _ as a class name. The new Java8 compiler complains that it \"might not be supported after Java SE 8\". I changed

Answer 1

Huh, you're right, using a $ in a classname works. Eclipse complains that it is against convention, but, if you are sure, you can do it.

The problem (conventionally) with using a $ is that the $ is used in the class hierarchy to indicate nested classes.... for example, the file A.java containing:

class A {
   class SubA {
   }
}

would get compiled to two files:

1. A.class
2. A$SubA.class

Which is why, even though $ works, it is ill advised because parsing the jars may be more difficult... and you run the risk of colliding two classes and causing other issues

EDIT, I have just done a test with the following two Java files (in the default package)

public class A {
    private static final class SubA {
        public String toString() {
            return "I am initializing Nested SUBA";
        }
    }

    private static final SubA sub = new SubA();
    public A() {
        System.out.println("What is " + sub.toString());
    }
}



public class A$SubA {
    @Override
    public String toString() {
        return "I am A$SubA";
    }
}


public class MyMain {
    public static void main(String[] args) {
        System.out.println(new A());
        System.out.println(new A$SubA());
    }
}

And the code will not compile.....

Two problems, type A$SubA is already defined, and can't reference a nested class A$SubA by it's binary name.