Sends a WARN log message and logs the exception. 
      Syntax
         
         
            public 
            void  
            w
            (
            final String 
            tag
            , 
            final Throwable 
            tr
            , 
            final String 
            location
            )
         
      
      Parameters
         
         
            - 
               tag – 
               Used to identify the source of a log message. It usually identifies the class or activity where the log call occurs.
            
 
            - 
               tr – 
               An exception to log
            
 
            - 
               location – 
               The line-level location of the log source (full class name of the class).