$1.$ The CustomRegister class should implement the Register interface and should have one class variable

of type HashMap named register. It should also contain the following methods:

CustomRegister$()$: It should initialize the class variable register with an empty HashMap.

void addAttendance$($int$[]$ a$)$: The array a contains the IDs of students. The attendance of a

student is equal to the number of times his$/$her ID occurs in a$.$ Add the attendances to the

register variable in the form