Chapter 8 Object-Based (Web hosting uk) Programming 337 Although setand
Chapter 8 Object-Based Programming 337 Although setand get accessors can provide access to privatedata, the access is restricted by the programmer s implementation of those methods. One form of software reuse is composition, in which a class contains as members references to objects of other classes. The thisreference is used implicitly and explicitly to refer to both the instance variables and the non-static methods of an object. The .NET Framework performs automatic garbage collection. Every class in C# can have a destructor that typically returns resources to the system. The destructor for an object is guaranteed to be called to perform termination housekeeping on the object just before the garbage collector reclaims the memory for the object (called finalization). In certain cases, all objects of a class should share only one copy of a particular variable. Programmers use static variables for this and other reasons. A static variable represents class-wide information all objects of the class share the same piece of data. The declaration of a static member begins with the keyword static. Such variables have class scope. A class s public static members can be accessed via the class name and the dot operator (e.g., Math.PI). A class s privatestatic members can be accessed only through methods or properties of the class. A method declared static cannot access non-static members. C# allows programmers to create constants whose values cannot change during program execution. To create a constant member of a C# class, the programmer must declare that member using either the constor readonly keyword. Members declared const must be initialized in the declaration; those declared with readonly can be initialized in the constructor, but must be initialized before they are used. Neither constnor readonly values can be modified once they are initialized. A class can define indexers to provide subscripted access to the data in an object of that class. Indexers can be defined to use any data type as the subscript. Each indexer can define a getand set accessor. Classes normally hide their implementation details from the clients of the classes. This is called information hiding. C# and the object-oriented style of programming elevate the importance of data. The primary activities of object-oriented programming in C# are the creation of data types (i.e., classes) and the expression of the interactions among objects of those data types. C# programmers concentrate on crafting new classes and reusing existing classes. Software reusability speeds the development of powerful, high-quality software. Rapid applications development (RAD) is of great interest today. Each class and interface in the .NET Framework belongs to a specific namespace (or library) that contains a group of related classes and interfaces. Namespaces provide a mechanism for software reuse. There is a good chance that the names you choose for classes will conflict with the names that other programmers choose for their classes. For this reason, namespaces provide a convention for unique class names.
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