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  1. JDK
  2. JDK-8013843

15.10.3: Array access for array-bounded capture variable

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      Description

      FULL PRODUCT VERSION :
      java version " 1.7.0_07 "
      Java(TM) SE Runtime Environment (build 1.7.0_07-b10)
      Java HotSpot(TM) 64-Bit Server VM (build 23.3-b01, mixed mode)


      ADDITIONAL OS VERSION INFORMATION :
      Darwin Chriss-MacBook-Pro.local 11.4.2 Darwin Kernel Version 11.4.2: Thu Aug 23 16:25:48 PDT 2012; root:xnu-1699.32.7~1/RELEASE_X86_64 x86_64

      A DESCRIPTION OF THE PROBLEM :
      Direct array element access (within a single line) of a wildcard generic type with an array typed upper bound fails with the following compilation error:

      GenericTest.java:6: error: array required, but CAP#1 found
      return foo.call()[0];
                       ^
        where CAP#1 is a fresh type-variable:
          CAP#1 extends Object[] from capture of ? extends Object[]
      1 error

      The fails for me on latest 1.7, 1.8 (recent lambda build) and 1.6 but compiles correctly in 1.5:
      java version " 1.5.0_30 "
      Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_30-b03-389-11M3811)
      Java HotSpot(TM) Client VM (build 1.5.0_30-161, mixed mode, sharing)


      REGRESSION. Last worked in version 5.0

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Attempt to compile the source code included with this report.

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      A successful compilation.
      ACTUAL -
      Compilation fails with a non-sensical error message.

      ERROR MESSAGES/STACK TRACES THAT OCCUR :
      GenericTest.java:6: error: array required, but CAP#1 found
      return foo.call()[0];
                       ^
        where CAP#1 is a fresh type-variable:
          CAP#1 extends Object[] from capture of ? extends Object[]
      1 error

      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      import java.util.concurrent.Callable;

      public class GenericTest {
        
          public Object foo(Callable<? extends Object[]> foo) throws Exception {
      return foo.call()[0];
          }
      }
      ---------- END SOURCE ----------

      CUSTOMER SUBMITTED WORKAROUND :
      The following class does compile successfully in all my versions of javac (1.5, 1.6, 1.7, 1.8 (recent lambda branch build):

      import java.util.concurrent.Callable;

      public class GenericTest {
        
          public Object foo(Callable<? extends Object[]> foo) throws Exception {
      Object[] array = foo.call();
      return array[0];
          }
      }

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              • Assignee:
                dlsmith Dan Smith
                Reporter:
                webbuggrp Webbug Group
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                Dates

                • Created:
                  Updated: