Object oriented programming (OOP) explained with an example

By Gaurab Banerji

Create a class that keeps track of a bank account balance. Then write a program to use this class.

Steps involved:

  • Run the class builder utility (SE24).

  • Create a class called ZACCOUNTxx, where xx is the last two digits of your logon ID.

  • Declare a PRIVATE attribute BALANCE of type DMBTR to store the account balance.

  • Create the following PUBLIC methods: 

    •  SET_BALANCE (Sets the balance to a new value)

      • IMPORTING NEW_BALANCE TYPE DMBTR 

    • DEPOSIT (Adds a deposit amount to the balance and returns the new balance)

      • IMPORTING AMOUNT TYPE DMBTR

      • RETURNING NEW_BALANCE TYPE DMBTR

    • WITHDRAW (Subtracts a deposit amount from the balance and returns the new balance.)

      • IMPORTING AMOUNT TYPE DMBTR

      • RETURNING NEW_BALANCE TYPE DMBTR

      • EXCEPTIONS INSUFFICIENT_FUNDS

  • Activate all elements of your class.

  • Write a program called Z_USE_ACCOUNT_xx, where xx is the last two digits of your logon ID. This program should do the following:

    • Instantiate an instance of the Account class.

    • Set the account balance to some initial value.

    • Make several deposits and withdrawals, printing the new balance each time. Do not allow the balance to become less than zero. (Use the exception to detect this.)

  • Test and debug your program. 

"Extra Credit": If you have extra time, try any of the following:

  • Replace the SET_BALANCE method with a constructor. Pass the opening balance when you instantiate the account object.

  • Create a static attribute and methods to set and get the name of the bank that holds the accounts.

Step-by-step approach with screen-shots

Go to SE24 (Class builder) 

Type in ZACCOUNTAA as the name of the class and press Create. 

 

Define 3 methods DEPOSIT, SET_BALANCE and WITHDRAW. 

 

Place the mouse cursor in DEPOSIT and hit the Parameters button. 

 

Write the parameters imported / exported for DEPOSIT method. 

Similarly for SET_BALANCE 

 

And WITHDRAW 

 

For withdraw we define an exception. 

 

We can see the attributes and methods by pressing “Display object list” button on top. 

 

Now we IMPLEMENT the 3 methods. Double click the method DEPOSIT. 

...Continued

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