Generics are used to have Typed Arrays.

Ex: if we have define that an array is confined to products.
if we push objects of product into array it accepts.
if we push employee objects into this array it will show
error . since the type of the array is product.

Generics was introduced in Framework 2.0
With generics we can have typed classes. While defining 
class we simply give placeholders and when we create 
objects of that class we declare the placeholder to be of 
some type(like int, double, string, etc.) and from that 
point on our object gets bind to that type only.