JDK-6508599 : 5.1.9: No unchecked conversion for array types
  • Type: Bug
  • Component: specification
  • Sub-Component: language
  • Affected Version: 6
  • Priority: P4
  • Status: Closed
  • Resolution: Fixed
  • Submitted: 2006-12-29
  • Updated: 2014-04-10
  • Resolved: 2011-07-21
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JDK 7
7 rcFixed
Related Reports
Relates :  
JDK-6558557 - Overhaul specification of unchecked casts
Relates :  
JDK-6557958 - 15.12.4.2: Specify unchecked conversion warning during variable-arity method invocation
Relates :  
JDK-8027284 - 5.1.9: Unchecked conversion for multidimensional arrays
Relates :  
JDK-6507024 - unchecked conversion between arrays fails after capture conversion
Description
The JLS does not define unchecked conversion for array types.  The compiler
has this conversion.  See 6507024.
Comments
EVALUATION Considering the example from 6507024: --- interface Result<T> {} <T> void m(Result<T>[] results) { Result<T>[] r = results.getClass().cast(null); } The type of results.getClass() is Class<? extends Result[]>. Consequently the type of results.getClass().cast(null) is the capture of ? extends Result[]. So the question is: is there there an unchecked conversion from the capture of ? extends Result[] to Result<T>[]? --- The capture of Class<? extends Result[]> is Class<#1> where ub(#1)=Result[] and lb(#1)=nulltype. The return type of cast(null) is #1. JLS3 5.1.9 should state that C[] becomes C<T>[] after unchecked conversion. This allows an unchecked conversion from #1 (morally, "Result[]") to Result<T>[]. Also, unchecked conversion applies only to raw types, and JLS3 technically does not allow array types to be raw. 4.8 should say: "More precisely, a raw type is defined to be one of: - The reference type that is formed by taking the name of a generic type declaration without any accompanying actual type parameters. - An array type whose element type is a raw reference type. - A non-static..."
26-09-2007