Generics - Bounded types

 Generics

Bounded Types

Sometimes it is useful to limit the types that can be passed to a type parameter. For example, a generic class that contains a method that returns the average of an array of numbers needs to restrict the data types to numeric data types only (integers, floats, and doubles). To handle such situations, Java provides bounded types. When specifying a type parameter, create an upper bound that declares the superclass from which all type arguments must be derived. This is accomplished through the use of an extends clause and / or interface type when specifying the type parameter, as shown here:

<T extends superclass>

<T extends superclass & interface>

 

// Generic programming

// Arrays - Bounded types

 

class Gen<T1 extends Number>

{

    T1 x[];

   

    Gen(T1 []v1)

    {

         x = v1;

    }

   

    public void fnDisplay()

    {

         System.out.println("Array elements");

         for(int i = 0;i<x.length;i++)

             System.out.println(x[i]);

    }

 

    public void fnAvg()

    {

         double sum = 0;

         for(int i = 0;i<x.length;i++)

             sum += x[i].doubleValue();

        

         System.out.println("Sum of elements = "+sum);

         System.out.println("Average of elements = "+(sum/x.length));

    }

}

 

class GenPgm4

{

    public static void main(String as[])

    {

         Integer [] ia = {2,4,6,8};

         Gen<Integer> g1 = new Gen<Integer>(ia);

         g1.fnDisplay();

         g1.fnAvg();

    }

}