What is the meaning of $ in a variable name?

Question

Recently, I found that $ is allowed in Java variable names, but has a special meaning. Unfortunately, it isn’t mentioned what this special meaning is.

So, my question is: What is the special meaning of $ in variable names in Java?

Here is the exact quote from 

Java: An Introduction to Problem Solving and Programming

From Walter Savitch:
 

Java does allow the dollar sign symbol $ to appear in an identifier, but these identifiers have a special meaning, so you should not use the $ symbol in your identifiers.

Answer 1

$ is used internally by the compiler to decorate certain names.

public class fool {

    class bar {

        public int x;

    }

    public void ozark () {

        Object f = new Object () {

            public String toString() {

                return "hello";

            }

        };

    }

}

Compiling this program will produce three .class files:

fool.class, containing the main class foo

fool$bar.class, containing the named inner class fool.bar

fool$1.class, containing the anonymous inner class

All of these class names are valid

Finally, the JLS recommends the following:

The $ character should be used only in mechanically generated source code or, rarely, to access preexisting names on legacy systems.

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