{"id":313,"date":"2023-05-11T09:38:48","date_gmt":"2023-05-11T07:38:48","guid":{"rendered":"https:\/\/oopm.org\/?page_id=313"},"modified":"2025-02-05T14:31:30","modified_gmt":"2025-02-05T13:31:30","slug":"3-1-using-class","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=313","title":{"rendered":"3.1 Using class"},"content":{"rendered":"
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Instead of describing each account object separately, we may describe a class<\/em> that defines a template\/pattern for accounts in general as i<\/mark>n the following example:<\/p>\n\n\n\n

class<\/strong> Account:\n   owner: val<\/strong> \"???\"\n   balance: var<\/strong> float\n   interestRate: var<\/strong> float\n   addInterest:\n      balance := balance + (balance * interestRate) \/ 100\n   deposit(amount: var<\/strong> float):\n      balance := balance + amount\n   withdraw(amount: var<\/strong> float) -> newB: var<\/strong> float:\n      balance:= balance - amount\n      newB := balance<\/code><\/pre>\n\n\n\n
The keyword class<\/strong><\/code> specifies that we describe a class as opposed to an object (using obj<\/code><\/strong>). <\/p>\n\n\n\n
We may use a class as a template to generate an arbitrary number of objects having the structure<\/em> as described by the class. All objects generated according to class Account<\/code> thus have the attributes that are described in class Account<\/code>. Each Account<\/code> object will thus have data-items owner<\/code> and balance<\/code> and methods addInterest<\/code>, deposit<\/code> and withdraw<\/code>. An Account<\/code> <\/em>object <\/em>is also referred to as an instance <\/em>of Account<\/code>.<\/p>\n\n\n\n
Different Account<\/code> objects will typically have different values of the data-items owner<\/code>, balance<\/code> and interestRate<\/code>. The methods in class Account<\/code> may be invoked on different Account<\/code> objects. <\/p>\n\n\n\n
We say that these objects are Account<\/code> objects<\/em> or instances of Account<\/code><\/em>.<\/p>\n\n\n\n
Before we show how to generate Account<\/code> object using class Account<\/code>, we have to fix a problem with the above description of class Account<\/code>. The problem is that the value of owner<\/code><\/font> is specified to be the string \"???\"<\/code>. John Smith and Liza Jones and other accounts have different values of owner<\/code>.<\/p>\n\n\n\n
To handle this, we may make owner<\/code> be a parameter of class Account<\/code>. The actual value of owner<\/code> must then be supplied when we create objects from class Account<\/code>. This is similar to how parameters works for methods as described in section