class Customer
{
     String name;
     Date   dob;
     .
     .

     Account[] accounts = new Account[5];
}

class Account
{
     int   accNo;
     float amount;
     .
     .
}

class Customer
{
     String name;
     Date   dob;
     .
     .
}

class Account
{
     Customer customer;
     int   accNo;
     float amount;
     .
     .
}

01/01 ------------ 04/30 -------------- 08/31 -------------- 12/31
* Account created  * Account            * Account            * Account
  and active         suspended            active               inactive

Account[] accounts = new Account[5];

public class Customer {
    // ...
    Set<Account> accounts = new HashSet<>();
}

public class Account {
    // ...
    Set<Customer> customers = new HashSet<>();
}

class CustomerClass
{
     int   CustNo;
     String name;
     Date   dob;
     .
     .
} // class CustomerClass

class AccountClass
{
     int   accNo;
     float amount;
     .
     .
} // class AccountClass

class AccountCustomerClass
{
     int   acccustNo;

  // How to relate both, added later
} // class AccountClass

class AccountClass
{
     int   accNo;
     decimal amount;
     .
     .
} // class AccountClass

class AccountCustomerClass
{
     int   accustNo;
     DateTime RegistrationDate;
     .
     .
     AccountClass Account;
} // class AccountClass

class CustomerClass
{
     int   CustNo;
     String name;
     Date   dob;
     .
     .
     AccountCustomerClass Accounts[];
} // class CustomerClass