Re: Generics warning message.

On Dec 30, 12:25 pm, Roedy Green <see_webs...@mindprod.com.invalid>
wrote:


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There might be a way. I think the following code performs a similar
function to what you are trying to achieve. The code compiles without
warnings or errors and it runs correctly. Nonetheless, it leaves
something to be desired.

import java . io . * ;
import java . util . * ;

class test
{
  public static void main ( String [ ] args ) throws Exception
  {
    ObjectInputStream ois = setupExample ( args ) ;
    runExample ( ois ) ;
  }

  /**
   * This just sets up the example.
   * It returns an appropriate ObjectInputStream
   * (i.e. one that has been stuffed with an ArrayList.
   **/
  private static ObjectInputStream setupExample ( String [ ] args )
    throws Exception
  {
    ArrayList < String > list = new ArrayList < String > ( ) ;
    for ( int i = 0 ; i < args . length ; i ++ )
      {
        list . add ( args [ i ] ) ;
      }
    ByteArrayOutputStream bos = new ByteArrayOutputStream ( ) ;
    ObjectOutputStream oos = new ObjectOutputStream ( bos ) ;
    oos . writeObject ( list ) ;
    oos . close ( ) ;
    bos . close ( ) ;
    byte [ ] b = bos . toByteArray ( ) ;
    ByteArrayInputStream bis = new ByteArrayInputStream ( b ) ;
    ObjectInputStream ois = new ObjectInputStream ( bis ) ;
    return ( ois ) ;
  }

  /**
   * This is the example.
   * We think that there is an ArrayList<java.lang.String> in
   * the InputStream.
   * How to cast it out without throwing warnings?
   **/
  private static void runExample ( ObjectInputStream ois ) throws
Exception
  {
    Object object = ois . readObject ( ) ;
    ArrayList list1 = ( ArrayList ) ( object ) ;
    ArrayList < String > list2 = nowarningCast ( String . class ,
list1 ) ;
    for ( String string : list2 )
      {
        System . out . println ( string ) ;
      }
  }

  /**
   * This is how I cast the ArrayList to
   * an ArrayList<java.lang.String> without
   * casting warnings.
   *
   * Take heed that this is not safe.
   **/
  private static < R > ArrayList < R > nowarningCast
    ( Class < R > clazz , ArrayList in )
  {
    ArrayList < R > out = new ArrayList < R > ( ) ;
    for ( Object val : in )
      {
        R r = clazz . cast ( val ) ;
        out . add ( r ) ;
      }
    return ( out ) ;
  }
}

Emory Merryman
External Concepts Guild
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