In reply to Anand Kumar C.R:
Constraint blocks are virtual, meaning when the constraint block in derived class has the same name as parent class, it would get override. I have modified the code, which works for your requirement !!
module polym_cons();
class parent;
rand int unsigned a;
constraint c1{
(a < 10);
}
endclass
class child extends parent;
constraint c1{
(a > 10);
}
endclass
parent parent_handle;
child child_handle = new();
initial
begin
parent_handle = child_handle;
parent_handle.randomize();
$display("a = %d",parent_handle.a);
end
endmodule