in a variable name in Java

Question

I am a beginner in Java. While looking at the naming conventions for variables it was mentioned that we can use "$" symbol in the variable name. Along with it, there was this line which said 

"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."

So can someone explain what is the special meaning behind $ symbol?

Answer 1

Java compiler uses "$" symbol internally to decorate certain names.

For Example:

public class demo {
    class test {
        public int x;
    }

    public void myTrial () {
        Object obj = new Object () {
            public String toString() {
                return "hello world!";
            }
        };
    }
}

Compiling this program will produce three .class files:

• demo.class, containing the main (outer) class demo
• demo$test.class, containing the named inner class demo.test
• demo$1.class, containing the anonymous inner class (local to method demo.myTrial)

The javac uses $ in some automatically-generated variable names for the implicitly referencing from the inner classes to their outer classes.​