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  1. JDK
  2. JDK-6714835

Safe cast is rejected (with warning) by javac

    Details

    • Subcomponent:
    • Resolved In Build:
      b120
    • CPU:
      x86
    • OS:
      linux
    • Verification:
      Verified

      Description

      FULL PRODUCT VERSION :
      java version "1.6.0"
      Java(TM) SE Runtime Environment (build 1.6.0-b105)
      Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

      A DESCRIPTION OF THE PROBLEM :
      Javac rejects a cast that is perfectly safe even without a warning.

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Compile attached program and observe that it fails

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      Should compile without warning.
      ACTUAL -
      Compiler rejects program

      ERROR MESSAGES/STACK TRACES THAT OCCUR :
      cast.java:4: incompatible types
      found : java.lang.Iterable<capture of ? extends java.lang.Number>
      required: java.util.Collection<? extends java.lang.Number>
        Collection<? extends Number> x2 = x1; // javac reports error here
                                          ^
      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      import java.util.*;
      class cast {
          Iterable<? extends Number> x1 = null;
          Collection<? extends Number> x2 = x1; // javac reports error here
      }

      ---------- END SOURCE ----------
      Actually the problem is the following (I checked with Neal Gafter, the submitter of this bug)

      import java.util.*;
      class cast {
         Iterable<? extends Number> x1 = null;
         Collection<? extends Number> x2 = (Collection<? extends Number>)x1; //javac generates a warning here
      }

      ACTUAL BEHAVIOR

      The output is (both 6-open and 6u06)

      $ javac Test.java -Xlint
      Test.java:4: warning: [unchecked] unchecked cast
      found : java.lang.Iterable<capture#156 of ? extends java.lang.Number>
      required: java.util.Collection<? extends java.lang.Number>
         Collection<? extends Number> x2 = (Collection<? extends Number>)x1; //javac generates a warning here
                                                                         ^
      1 warning

      EXPECTED BEHAVIOR

      The program should compile without any warning.

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