{"id":871,"date":"2023-09-01T15:52:36","date_gmt":"2023-09-01T13:52:36","guid":{"rendered":"https:\/\/oopm.org\/?page_id=871"},"modified":"2025-01-12T13:34:09","modified_gmt":"2025-01-12T12:34:09","slug":"2-7-using-the-account-object","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=871","title":{"rendered":"2.8 The second program"},"content":{"rendered":"
\"image_pdf\"<\/a>\"image_print\"<\/a><\/div>\n

In this section, we show how to represent activities of a clerk in the bank system. We may do this by introducing an object representing a clerk. In the example, the clerk makes a few transactions on the account_1010<\/code>:<\/p>\n\n\n\n

aClerk: obj<\/strong>\n   handle:\n      newBalance: var<\/strong> float\n      account_1010.interestRate := 0.7\n      newBalance := account_1010.deposit(100)   \n      newBalance := account_1010.deposit(225)\n      account_1010.addInterest\n      newBalance := account_1010.withdraw(111)\n      console.print(\"The new balance is:\" + newBalance) <\/code><\/pre>\n\n\n\n
The activities of the clerk is represented by a method, handle<\/code>, of the aClerk<\/code> object. The description of the method handle<\/code> consists of the following items:<\/p>\n\n\n\n
    \n
  1. A declaration of a local variable newBalance<\/code>.<\/li>\n\n\n\n
  2. An assignment statement account_1010.interestRate := 0.7<\/code>.<\/li>\n\n\n\n
  3. Two invocations of the deposit<\/code> method on account_1010<\/code>, with arguments 100<\/code> and 225<\/code>.\n
      \n
    • The balance<\/code> is now 325<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • An invocation of the addInterest<\/code> method on account_1010<\/code>.\n
        \n
      • The balance<\/code> is now 325 + 325 * 0.7% = 327,28<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • An invocation of withdraw<\/code> on account_1010<\/code> with argument 111<\/code>.\n
          \n
        • The balance<\/code> is now 216,28<\/li>\n<\/ul>\n<\/li>\n\n\n\n
        • And finally, a statement printing the new balance<\/code> of the account.<\/li>\n<\/ol>\n\n\n\n
          As mentioned, objects exist within a computer, and the bank clerks need to be able to manipulate the objects. In order to do this, a given object model must be able to receive information from outside the computer and to deliver information to the outside. This is called input<\/em> and output<\/em> (abbreviated I\/O<\/em>) to and from an object model.<\/p>\n\n\n\n
          As a simple start on handling I\/O, we assume that our system has an object\u00a0console<\/code>\u00a0that represents a window on the screen of the computer executing the bank system. The console<\/code> object has a method print<\/code> for printing strings and numbers in the associated window.<\/p>\n\n\n\n
          The clerk executes the following statement as part of handle<\/code>:<\/p>\n\n\n\n
          console.print(\"The new balance is: \" + newBalance)<\/code><\/pre>\n\n\n\n