{"id":315,"date":"2023-05-11T09:40:08","date_gmt":"2023-05-11T07:40:08","guid":{"rendered":"https:\/\/oopm.org\/?page_id=315"},"modified":"2025-01-16T06:49:07","modified_gmt":"2025-01-16T05:49:07","slug":"3-2-references","status":"publish","type":"page","link":"https:\/\/oopm.org\/?page_id=315","title":{"rendered":"3.3 Introducing a Customer class"},"content":{"rendered":"
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Customers of a bank and thereby potential owners of an account will usually have a profile with more than just the name (like “John Smith”). In addition, the same customer may have more than one account in the bank, and there may be other situations where the profile of a customer is needed.<\/p>\n\n\n\n

With classes of objects, the way to model this is to introduce the class Customer<\/code> with attributes representing the properties of a customer profile.<\/p>\n\n\n\n

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class<\/strong> Customer(name: var<\/strong> String):\n   addr: var<\/strong> String         \n   email: var<\/strong> String<\/code><\/pre>\n<\/div>\n\n\n\n
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We may declare a Customer<\/code> object as follows:<\/p>\n\n\n\n
JohnSmithProfile: obj<\/strong> Customer(\"John Smith\")<\/code><\/pre>\n\n\n\n
We may subsequently assign values to the data-items addr<\/code> and email<\/code> of JohnSmith<\/code>:<\/p>\n\n\n\n
JohnSmithProfile.addr := \"1011 Eagle Road, Moon Town, Utopia\"\nJohnSmithProfile.email := \"john.smith@utopia.org\"<\/code><\/pre>\n\n\n\n
We would like to be able to refer to the JohnSmithProfile<\/code>-object from the Account<\/code> object. In order to handle this, we introduce the mechanism of a variable reference<\/em>, which may be declared as follows:<\/p>\n\n\n\n
aCustomer: ref<\/strong> Customer    <\/code><\/pre>\n\n\n\n
The variable, aCustomer<\/code> may refer to different Customer<\/code>-objects during program execution. While the data-items we have seen so far (balance<\/code> and interestRate<\/code>) may hold different float<\/code> values representing different values of balance<\/code> and interestRate<\/code>, the data-item aCustomer<\/code> is a reference data-item that may refer to Customer<\/code> objects.<\/p>\n\n\n\n
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We may e.g. set aCustomer<\/code> to refer to the JohnSmithProfile<\/code>-object using an assignment statement:<\/p>\n<\/div>\n\n\n\n
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aCustomer := JohnSmithProfile<\/code><\/pre>\n<\/div>\n<\/div>\n\n\n\n