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  1. JDK
  2. JDK-4098167

Use of '$' by inner classes conflicts with uses permitted by JLS

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: P4
    • Resolution: Won't Fix
    • Affects Version/s: 1.2.0, 1.3.0
    • Fix Version/s: None
    • Component/s: specification
    • Labels:
    • Subcomponent:
    • CPU:
      generic, x86
    • OS:
      generic, windows_nt, windows_2000

      Description

      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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              Assignee:
              abuckley Alex Buckley
              Reporter:
              wmaddoxsunw William Maddox (Inactive)
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