Generics - Bounded types

 Generics and Bounded types

Generics

Generics means parameterized types.

Parameterized types enable users to create classes, interfaces, and methods in which the type of data upon which they operate is specified as a parameter.

Using generics, it is possible to create classes that automatically work with different types of data.

A class, interface, or method that operates on a parameterized type is called generics.

// Generic programming – Example

// T1 – Type Parameter

// T1 – will be replaced by real type when object is created

 

class Gen<T1>

{

     T1 x;

    

     Gen(T1 v)

     {

          x = v;

     }

    

     public void fnDisplay()

     {

          System.out.println("x = "+x);

          System.out.println("Data type = "+x.getClass().getName());

     }

}

 

class Generics_Demo

{

     public static void main(String as[])

     {

          Gen<Integer> g1 = new Gen<Integer>(5);

          g1.fnDisplay(); 

         

          Gen<Double> g2 = new Gen<Double>(4.5);

          g2.fnDisplay(); 

         

          Gen<String> g3 = new Gen<String>("asd");

          g3.fnDisplay(); 

     }

}

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 Generics_Demo

{

     public static void main(String as[])

     {

          Integer [] ia = {2,4,6,8};

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

          g1.fnDisplay(); 

          g1.fnAvg();

     }

}