Two recent bug reports (4096303 and 4094180) have once again raised
issues concerning the use of '$' characters in Java identifiers.  The
JLS states that "The '$' character should be used only in mechanically
generated Java code or, rarely, to access pre-existing names on legacy
systems."  Thus, although discouraged in ordinary usage, the compiler
cannot rule out such names, and the reservation of certain names by the
inner class mechanism is indeed an incompatible change to the Java
language (as it existed prior to 1.1) that must be precisely defined.

The following program illustrates three of the ways in which a name
appearing in Java source can conflict with a name generated implicitly
by the compiler according to the inner classes specification:

	class C {
	  class N {
	    int this$0;		//BAD
	  }
	}
	class C$N { }		//BAD

	class Baz {
	  void quux() {
	     class Quem {}
	     }
	}
	class Baz$1$Quem {}	//BAD

It is not sufficient merely to advise users against using '$' in
identifiers, as we must offer guidance to those who are writing
automatic program generators for whom we have ostensibly reserved such
names.

william.maddox@Eng 1997-12-09


Name: skT45625			Date: 05/10/2000


java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0-C)
Java HotSpot(TM) Client VM (build 1.3.0-C, mixed mode)

Starting with JDK 1.3, javac breaks on "this$0" references. Try compiling the
following example:

public class TestInner {

    public class Inner {

	public void test() {
	    System.out.println("My outer class: "+this$0);
	}
    }

    public void test() {
	Inner inner = new Inner();
	inner.test();
    }

    static public void main(String[] args) {
	TestInner inner = new TestInner();
	inner.test();
    }
}

C:\Current\Server>javac *.java
TestInner.java:6: cannot resolve symbol
symbol  : variable this$0
location: class TestInner.Inner
            System.out.println("My outer class: "+this$0);
(Review ID: 104660)
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