Why use printf("%s") for arguments passed to generic methods?

Question

package genericMethods;

public class OverloadedMethods {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Integer[] integerArray = {1, 2, 3, 4, 5};
        Double[] doubleArray = {1.0, 2.0, 3.0, 4.0, 5.0};
        Character[] charArray = {'a', 'b', 'c', 'd'};

        System.out.println("A has: ");
        printArray(integerArray);
        System.out.println("B has: ");
        printArray(doubleArray);
        System.out.println("C has: ");
        printArray(charArray);
    }

    public static <T> void printArray(T[] array)
    {
        for(T element : array)
            System.out.printf("%s ", element);//why use %s instead of others? 

        System.out.println();
    }

}

My question is the method printArray() doesn't know what type of data is going to print out, and seems %d will occur error at run time - but isn't %s for String only ?

Answer 1

The issue is that you don't KNOW what type "element" will be. In your example, it could be Integer, Double, or Character. That being the case, you can't use %d or %lf, because those wouldn't work for types that aren't Integer (for %d) or Double (for %lf).

%s actually works for them all, because all Object types have a .toString(), so they can all be converted to Strings for printing.

Answer 2

The use of %s will result in the toString() method being called on the object, and thus will work for any type T.