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class10 Notes

class10 Notes - 1 1 IST 240 Thu(2/14 ¢ Ch 5 More classes...

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Unformatted text preview: 1 1 IST 240 ¡ Thu (2/14) ¢ Ch 5: More classes ¢ In-class exercise ¡ Done via extreme programming method ¢ Hwk #5 ¡ Ch 5: due Wed 2/20 at 11:59pm ¢ Ex 5.1, 5.3, 5.11, 5.13 ¢ PP 5.5 ¡ Tue (2/19) ¢ UML Introduction + more classes ¡ Thu (2/21) ¢ Ch 6: Introduction to Graphical User Interfaces (GUIs) 2 5.3 – Encapsulation ¡ We can take one of two views of an object ¢ internal - the details of the variables and methods of the class that defines it ¢ external - the services that an object provides and how the object interacts with the rest of the system ¡ From the external view, an object is an encapsulated entity, providing a set of specific services ¡ These services define the interface to the object 2 3 5.3 – Encapsulation ¡ One object (called the client ) may use another object for the services it provides ¡ The client of an object may request its services (call its methods), but it should not have to be aware of how those services are accomplished ¡ Any changes to the object's state (its variables) should be made by that object's methods ¡ We should make it difficult, if not impossible, for a client to access an object’s variables directly ¡ That is, an object should be self-governing 4 5.3 – Encapsulation ¡ An encapsulated object can be thought of as a black box – its inner workings are hidden from the client ¡ The client invokes the interface methods of the object, which manages the instance data Methods Data Client 3 5 5.3 – Visibility Modifiers ¡ In Java, we accomplish encapsulation through the appropriate use of visibility modifiers ¡ A modifier is a Java reserved word that specifies particular characteristics of a method or data ¡ We've used the final modifier to define constants ¡ Java has three visibility modifiers: public , protected , and private ¡ The protected modifier involves inheritance, which we will discuss later 6 5.3 – Visibility Modifiers public private Variables Methods Provide services to clients Support other methods in the class Enforce encapsulation Violate encapsulation 4 7 5.3 – Accessors and Mutators ¡ Because instance data is private, a class usually provides...
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class10 Notes - 1 1 IST 240 Thu(2/14 ¢ Ch 5 More classes...

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