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  1. JDK
  2. JDK-6728196

At runtime a referenced object can not be an interface type (aastore,checkcast,instanceof)

    Details

    • Subcomponent:
      vm
    • CPU:
      generic
    • OS:
      generic

      Description

      The following specification parts in Byte Code section (ie.
      aastore,checkcast,instanceof) define rules to the case
      where a referenced object is an interface type.
      However, at runtime an referenced object can not be an interface type but a class
      type because an object can not be created from an interface (see the definition
      of 'new' byte code) but an object can be created from a class.
      So, the following specification parts saying about the case of "interface type"
      may be not appropriate for runtime behavior.

      Any guidance to our licensees about how to implement the speficiation part
      would be appreciated.

      === instanceof ===========================================

      instanceof
      <snip>

       Format

          instanceof
          indexbyte1
          indexbyte2

      Forms

          instanceof = 193 (0xc1)

      Operand Stack

          ..., objectref ..., result

      Description

      <snip>

          The following rules are used to determine whether an objectref
          that is not null is an instance of the resolved type: If S is the class of
          the object referred to by objectref and T is the resolved class, array,
          or interface type, instanceof determines whether objectref is an instance
          of T as follows:

      <snip>

      ----------> The following parts are not appropriate.

          * If S is an interface type, then:

                o If T is a class type, then T must be Object (¿2.4.7).

                o If T is an interface type, then T must be the same interface as S,
                  or a superinterface of S (¿2.13.2).

      === checkcast ============================================

      checkcast

      <snip>

          Format

          checkcast
          indexbyte1
          indexbyte2

      Forms

          checkcast = 192 (0xc0)

      Operand Stack

          ..., objectref ..., objectref

      Description

       <snip>

         The following rules are used to determine whether an objectref
         that is not null can be cast to the resolved type: if S is
         the class of the object referred to by objectref and T is
         the resolved class, array, or interface type, checkcast determines
         whether objectref can be cast to type T as follows:

      <snip>

      ----------> The following parts are not appropriate.

          * If S is an interface type, then:

                o If T is a class type, then T must be Object (¿2.4.7).

                o If T is an interface type, then T must be the same interface as S
                  or a superinterface of S (¿2.13.2).

      === aastore =============================================

      aastore

      <snip>

          Format

          aastore

      Forms

          aastore = 83 (0x53)

      Operand Stack

          ..., arrayref, index, value ...

      Description
      <snip>

          The type of value must be assignment compatible (¿2.6.7) with
          the type of the components of the array referenced by arrayref.
          Assignment of a value of reference type S (source) to a variable
          of reference type T (target) is allowed only when the type S supports
          all the operations defined on type T. The detailed rules follow:

      <snip>

      ----------> The following parts are not appropriate.

          * If S is an interface type, then:

                o If T is a class type, then T must be Object (¿2.4.7).

                o If T is an interface type, then T must be the same interface
                  as S or a superinterface of S (¿2.13.2).

      =======================================================

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            • Assignee:
              abuckley Alex Buckley
              Reporter:
              eijsuzuk Eiji Suzuki
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              • Created:
                Updated:
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