overloading generic methods

[Mike Mitchell]

Hi guys. I have two questions about generic method overloading.

With regard to this code:

public class GenericOverloads {
 
    public static void main(String[] args) {
 
        OverloadMe("dogs", "cats", "apples"); // call 1
        //OverloadMe(1, 2, 3); // call 2
        OverloadMe(new Integer(1), new Integer(2), new Integer(3)); // call 2a
        OverloadMe(1.1, 2.2, 3.3); // call 3
        OverloadMe(new Float(1.1), new Float(2.2), new Float(3.3)); // call 3a
    }
    
    /*
    // method 1
    private static <T extends Comparable<T>> void OverloadMe(T x, T y, T z) {
        System.out.println("OverloadMe 1 (" + x + "," + y + "," + z + ")");
    }
    */
    
    // method 2
    private static void OverloadMe(String x, String y, String z) {
        System.out.println("OverloadMe 2 (" + x + "," + y + "," + z + ")");    
    }
        
    // method 3
    private static <T extends Number> void OverloadMe(T x, T y, T z) {
        System.out.println("OverloadMe 3 (" + x + "," + y + "," + z + ")");
    }
    
    // method 4
    private static <T extends Integer> void OverloadMe(T x, T y, T z) {
        System.out.println("OverloadMe 4 (" + x + "," + y + "," + z + ")");
    }
}
 

(a) When methods 1 and 3 are commented in, compiler complains about 'call 2', presumably because Number implements Comparable. If I comment out 'method 1', the compiler chooses the method with the narrower upper bound. Is there a rule about overloading generic methods to be deduced from that? Does this have something to do with 'covariance'?

(b) When methods 3 and 4 are commented out the autoboxing of calls 2 and 3 works fine, however when 3 and 4 are in (and method 1 out per a), call 2 fails with:

  
symbol  : method valueOf(int)
location: bound of type variable T
        OverloadMe(1, 2, 3); // call 2
Fatal Error: Unable to find method valueOf

and call 3 with:

.../GenericOverloads.java:18:internal error; cannot instantiate
<T>OverloadMe(T,T,T) at scratch.GenericOverloads to 
(double,double,double)
        OverloadMe(1.1, 2.2, 3.3); // call 3
1 error

If I explicitly box them myself it works as expected. That seems strange to me.

Thanks.
[ June 21, 2008: Message edited by: Mike Mitchell ]