Question

I’m working on something related to generics in java and I’ve found this example on the internet here. This might be a simple question but I want to find a correct answer from someone who worked with generics. This generic method takes as input argument different types of arrays and displays them. Now I want to do this by reading those arrays from command line. Can you please help me find the correct way to do it? Thanks.

public class GenericMethodTest
    {
       // generic method printArray                         
       public static < E > void printArray( E[] inputArray )
       {
          // Display array elements              
             for ( E element : inputArray ){        
                System.out.printf( "%s ", element );
             }
             System.out.println();
        }

        public static void main( String args[] )
        {
            // Create arrays of Integer, Double and Character
            Integer[] intArray = { 1, 2, 3, 4, 5 };
            Double[] doubleArray = { 1.1, 2.2, 3.3, 4.4 };
            Character[] charArray = { 'H', 'E', 'L', 'L', 'O' };

            System.out.println( "Array integerArray contains:" );
            printArray( intArray  ); // pass an Integer array

            System.out.println( "\nArray doubleArray contains:" );
            printArray( doubleArray ); // pass a Double array

            System.out.println( "\nArray characterArray contains:" );
            printArray( charArray ); // pass a Character array
        } 
    }

Answer 1

I think you will have to include the datatype as part of your command line, or else have a routine which detects the type by heuristics. Something like

java GenericMethodTest "doubleArray" "1.1 2.2"

where you have two args, the type and the array. Then you will need a constructor which converts the second argument from a string to an array, such as

public DoubleArray (String sin) {
    String[] ss = sin.split(" ")'
    double dd[] = new Double[ss.length];
    for (String s : ss) {
        dd[i++] = new Double(s);
    }
}

I do this sort of thing a lot in scientific programming and I usually end up with special cases for the datatypes. How does the program know what is an integer or a string or a double? You either have to tell it or you have to give it a chance to guess.