Bounded Types

Bounded Types

• While creating objects to generic classes we can pass any derived type as type parameters.

• Many times it will be useful to limit the types that can be passed to type parameters. For that purpose, bounded types are introduced in generics.

• Using bounded types, we can make the objects of generic class to have data of specific derived types.

• For example, If we want a generic class that works only with numbers (like int, double, float, long .....) then declare type parameter of that class as a bounded type to Number class. Then while creating objects to that class you have to pass only Number types or it's subclass types as type parameters.

The syntax for declaring Bounded type parameters is

<T extends SuperClass>

• This specifies that 'T' can only be replaced by 'SuperClass' or it's sub classes.

• For example

class Test<T extends Number> //Declaring Number class as upper bound of T

{

T t;

public Test(T t)

{

this.t = t;

}

public T getT()

{

return t;

}

}

public class BoundedTypeDemo

{

public static void main(String[] args)

{

//Creating object by passing Number as a type parameter

Test<Number> obj1 = new Test<Number>(123);

System.out.println("The integer is: "+obj1.getT());

//While Creating object by passing String as a type parameter, it gives compile time //error

Test<String> obj2: = new Test<String>("I am string"); //Compile time error

System.out.println("The string is: "+obj2.getT());

}

}

Review Question

1. Explain the use of bounded types in Generics with illustrative program.