Hello Ashu,
The association describes a property of a class, i.e. type of a property, multiplicity relationship and etc.
In your example, you have two properties belonging to the class A, i.e.
B b[] = new B1()
B b = new B2()
These two properties have the same type ( B ), but different multiplicity relationships. As a result, on your class diagram you will show two associations between class A and class B with different multiplicities. You do not need to show the association relationship between two implementation classes of class B, since these are not the types of your properties.
Janis
SCEA 5.0, SCBCD 5.0, SCWCD 1.4, SCJP 5.0
OMG-Certified UML Professional, Intermediate; OMG-Certified UML Professional, Fundamental