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  1. JDK
  2. JDK-6938454

Unable to determine generic type in program that compiles under Java 6

    Details

    • Subcomponent:
    • Resolved In Build:
      b105
    • CPU:
      x86
    • OS:
      windows_2008
    • Verification:
      Verified

      Description

      FULL PRODUCT VERSION :
      java version "1.7.0-ea"
      Java(TM) SE Runtime Environment (build 1.7.0-ea-b86)
      Java HotSpot(TM) 64-Bit Server VM (build 17.0-b10, mixed mode)

      ADDITIONAL OS VERSION INFORMATION :
      Microsoft Windows [Version 6.1.7600]

      A DESCRIPTION OF THE PROBLEM :
      Code that compiles under Java 6 no longer compiles under the latest Java 7 release.

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Compile the test program.

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      The program should compile.
      ACTUAL -
      Fails to compile.

      ERROR MESSAGES/STACK TRACES THAT OCCUR :
      Test.java:17: type parameters of <T>T cannot be determined; no unique maximal instance exists for type variable T with upper bounds SpecialKey,K
                              m_key = makeKey(m_key);
                                             ^
        where T,K are type-variables:
          T extends K declared in method <K,T>makeKey(K)
          K extends Key declared in method <K,T>makeKey(K)
      Note: Test.java uses unchecked or unsafe operations.
      Note: Recompile with -Xlint:unchecked for details.
      1 error

      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      abstract class Key
      {
      }

      class SpecialKey extends Key
      {
      }

      public class Test
      {
      private SpecialKey m_key;

      public SpecialKey getKey()
      {
      if (m_key == null)
      {
      m_key = makeKey(m_key);
      }

      return m_key;
      }

      private static <K extends Key, T extends K> T makeKey(K pk)
      {
      return (T)new SpecialKey();
      }
      }
      ---------- END SOURCE ----------

      Release Regression From : 6
      The above release value was the last known release where this
      bug was not reproducible. Since then there has been a regression.

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            • Assignee:
              mcimadamore Maurizio Cimadamore
              Reporter:
              ndcosta Nelson Dcosta
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              • Created:
                Updated:
                Resolved:
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