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Topic: Abstract class

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	Abstract Class - qtnode
		An Abstract Class is a class that cannot be implemented directly but must be inherited by a superior class.
		An abstract class is created by creating at least one virtual member function with a 0 (zero) initializer.
		In some cases, the abstract class would have to be modified to include additional skeleton framework (pure virtual functions), or the superior class will simply take care of the implementation details directly.
	qtnode.net /wiki/Abstract_Class (473 words)

	Xah: The “abstract” keyword in Java
		Abstract class does not necessarily require its methods to be all abstract.
		That is to say: abstract class is a parent for a collection of sub classes, where itself declares certain methods but doesn't define any implementations.
		Their similarity, is that both interface and abstract class require the child class to have the methods set.
	xahlee.org /java-a-day/abstract_class.html (785 words)

	PracticalEmbeddedJava
		Abstract classes are useful when you want to encapsulate a set of common features in one superclass, and you want some concrete methods in the superclass itself.
		A subclass of an abstract class can only be instantiated if it overrides each of the abstract methods of the superclass and provides an implementation for each of them.
		If an abstract class doesn't implement all of the superclass methods, then it is also abstract (and therefore can't be instantiated).
	www.systronix.com /book/language/AbstractClasses.html (971 words)

	Abstract Classes in VB .NET
		An abstract class is designed to act as a base class (to be inherited by other classes).
		Abstract class is a design concept in program development and provides a base upon which other classes are built.
		Members of an abstract class can either be Overridable (all the inheriting classes can create their own implementation of the members) or they can have a fixed implementation that will be common to all inheriting members.
	www.startvbdotnet.com /oop/abstract.aspx (240 words)

	JAVA GLOSSARY, Abstract Class
		Abstract class is used to specify that a class is not to be instantiated, but rather inherited by other classes.
		An abstract class can have abstract methods that are not implemented in the abstract class, but in subclasses.
		Because an abstract class is not fully defined you cannot declare abstract constructors, or abstracr static methods.
	www.allapplabs.com /glossary/abstract_class.htm (158 words)

	Abstract Methods and Classes (The Java™ Tutorials > Learning the Java Language > Interfaces and Inheritance)
		When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.
		Such abstract classes are similar to interfaces, except that they provide a partial implementation, leaving it to subclasses to complete the implementation.
		A single abstract class is subclassed by similar classes that have a lot in common (the implemented parts of the abstract class), but also have some differences (the abstract methods).
	java.sun.com /docs/books/tutorial/java/IandI/abstract.html (561 words)

	abstract (C#)
		Members marked as abstract, or included in an abstract class, must be implemented by classes that derive from the abstract class.
		It is not possible to modify an abstract class with the sealed (C# Reference) modifier, which means that the class cannot be inherited.
		An abstract inherited property can be overridden in a derived class by including a property declaration that uses the override modifier.
	msdn2.microsoft.com /en-us/library/sf985hc5.aspx (409 words)

	abstract from FOLDOC
		Examples are abstract data types (the representation details are hidden), abstract syntax (the details of the concrete syntax are ignored), abstract interpretation (details are ignored to analyse specific properties).
		Such abstract machines are not intended to be constructed as hardware but are used in thought experiments about computability.
		A parse tree is similar to an abstract syntax tree but it will typically also contain features such as parentheses which are syntactically significant but which are implicit in the structure of the abstract syntax tree.
	foldoc.org /?abstract (1438 words)

	Testing Interfaces (Site not responding. Last check: 2007-10-20)
		It is common for a single interface or abstract class to have many different descendants or implementations.
		We are encoding the functional correctness criteria of the interface or abstract class in the test and then applying that criteria to the implementations of the interface.
		Once the interface or abstract class is specified, we need to write a JUnit test case that will test the functional compliance of any class that implements this interface.
	www.placebosoft.com /abstract-test.html (1838 words)

	Abstract and Sealed Classes and Class Members (C#)
		The abstract keyword enables you to create classes and class members solely for the purpose of inheritance—to define features of derived, non-abstract classes.
		The sealed keyword enables you to prevent the inheritance of a class or certain class members that were previously marked virtual.
		For example, a class library may define an abstract class that is used as a parameter to many of its functions, and require programmers using that library to provide their own implementation of the class by creating a derived class.
	msdn2.microsoft.com /en-us/library/ms173150.aspx (501 words)

	PHP: Class Abstraction - Manual
		When inheriting from an abstract class, all methods marked abstract in the parent's class declaration must be defined by the child; additionally, these methods must be defined with the same (or weaker) visibillity.
		For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public.
		Abstract classes allow the declaration of protected abstract methods, which cannot be emulated with the use of an interface and a concrete superclass.
	www.php.net /manual/en/language.oop5.abstract.php (503 words)

	Abstract Class Definitions
		Since abstract classes do not define objects, and do not contain shared attributes or constants, such calls on the class are not meaningful.
		In this illegal abstract class, A and B do not conflict because their arguments are concrete and are not the same type.
		However, because the argument of C is abstract and unrelated it conflicts with both A and B. D does not conflict with A, B or C because it has a different number of parameters.
	www.gnu.org /software/sather/docs-1.2/tutorial/abstract1223.html (405 words)

	nodename » From C++ to ActionScript 2.0, 4: Abstract Classes
		For a comparison of abstract classes and interfaces, and what they’re good for, have a look at Java Glossary: Interface vs Abstract Class, just about all of which (except for the stuff about "static final constants") is applicable to ActionScript as well, once we implement abstract classes.
		Unlike in C++, the only way we could implement Abstract’s methodThree at compile time would be to define it in the class body, but then it would no longer be abstract, and a derived class could get away without overriding it.
		To ensure cross-compiler compatibility, all abstract members are defined with empty class member stubs - these are removed automatically by the compiler and the compiler then fully checks both constructor access and the parent hierarchy to ensure that all declared abstract members and missing interface methods are implemented in the concrete class.
	nodename.com /blog/2005/09/19/abstract-classes (1029 words)

	Abstract class Vs Interface
		Abstract classes have atleast one method abstract and interfaces have all abstract methods.
		Abstract classes can be used to inherit implementation.
		Not all methods in an Abstract class are abstract themselves, and you can also pass along some hidden data members.
	forum.java.sun.com /thread.jspa?threadID=582104&messageID=2962845 (989 words)

	Abstract classes
		Abstract type names and class names are similar, but the letters must be uppercase and abstract type names begin with '$'.
		There must be no cycle of abstract types such that each appears in the subtype list of the next, ignoring the values of any type parameters but not their number.
		There must be no cycle of abstract classes such that each class appears in the supertype list of the next, ignoring the values of any type parameters but not their number.
	www.gnu.org /software/sather/docs-1.2/specification/abstractclasses.html (708 words)

	Abstract Classes (Visual Basic and Visual C# Concepts)
		One key difference between abstract classes and interfaces is that a class may implement an unlimited number of interfaces, but may inherit from only one abstract (or any other kind of) class.
		A class that is derived from an abstract class may still implement interfaces.
		Abstract classes are useful when creating components because they allow you specify an invariant level of functionality in some methods, but leave the implementation of other methods until a specific implementation of that class is needed.
	msdn.microsoft.com /library/en-us/vbcon/html/vbconabstractclasses.asp?frame=false (403 words)

	Visual Case - UML Tutorial - Class Diagram
		In Visual Case, classes shown on a diagram that do not belong to the same package as the diagram are shown with their entire path name.
		Not all of the operations in an abstract class have to be abstract.
		Fortunately class diagrams closely relate to the most object oriented languages, so the basics (classes, operations, attributes, generalizations, etc.) should be fairly easy to grasp.
	www.visualcase.com /tutorials/class-diagram.htm (1713 words)

	Zend Technologies - PHP 5 Core Basics - Working with Class Types: Abstract Classes and Interfaces (Site not responding. Last check: 2007-10-20)
		In implementing abstract methods, you must define the same number of arguments, reproduce any type hinting in the argument list, and ensure that the implementing method's access level (public, protected or private) is no stricter than that defined in the abstract parent.
		PHP 5 enforces abstract classes when the script is first parsed, so a failure to implement an abstract method is picked up right away.
		Abstract classes and interfaces can be used to separate interface from implementation, eliminating tangles of conditional code, and grouping related functionality together.
	www.zend.com /php5/articles/php5-interfaces.php (2237 words)

	Abstract Classes in PHP: Introducing the Key Concepts
		By the end of this series, you should have a better idea of how abstract classes fit into the development of certain applications, and hopefully you’ll be equipped with the knowledge to decide how and when to put them to work for you.
		In the simplest sense, an abstract class is a class that cannot (and should not) be instantiated.
		To cite a case where an abstract class can be useful, allow me illustrate a typical situation: you’re developing an application where different classes are organized in a well-structured hierarchy.
	www.devshed.com /c/a/PHP/Abstract-Classes-in-PHP-Introducing-the-Key-Concepts (1900 words)

	Class Diagrams
		The class diagram depicts the public interface of a single class and the other classes it uses or is used by.
		The name and methods of abstract classes are written in italics, and those of concrete classes appear in the normal font.
		An aggregation (or composition) relation is shown by an arrow from the composing class to the composed class.
	www.prenhall.com /divisions/esm/app/kafura/secure/chapter9/html/classd_3.htm (959 words)

	Class java.lang.ClassLoader
		However, some classes may not originate from a file; they may originate from other sources, such as the network, or they could be constructed by an application.
		Class loaders should use a hashtable or other cache to avoid defining classes with the same name multiple times.
		A system class is a class loaded from the local file system in a platform- dependent way.
	web.mit.edu /java_v1.1.5/www/api/java.lang.ClassLoader.html (973 words)

	Abstract Class
		You are implementing a New Class and discover that you are adding methods that are identical to those in an already existing sibling class.
		It is common for an abstract class to define the common representation and/or behaviour of its concrete subclasses.
		These stub methods in the abstract class demonstrate the method protocol that the subclasses must provide and serve as a placeholder for Method Comments describing the protocol.
	www.object-arts.com /docs/abstractclass.htm (314 words)

	Abstract class ...
		However, note that you won't be able to instantiate the abstract class, even though it lacks any abstract methods; you still must extend from it before you can use it.
		Abstract classes are used when you are designing a class hierarchy and you want to create a base class that other classes can be derived from, but you don't ever want an instance of that class instantiated.
		It's an abstract class that is used as the base class for both the ArrayList and Vector classes, and is described as being a skeletal implementation of the List interface to minimize the effort required to implement this Interface.
	www.javalobby.org /java/forums/t16348.html (372 words)

	Abstract Static Variables
		You are in the process of abstracting common methods, algorithms and data structures into an abstract class.
		The type of the class constant might not be a data primitive and subsequent sub-classes may also wish to over-ride the constant of the first generation sub-class.
		Abstracting the common code to the super-class would significantly reduce the size, the complexity and the difficulty of maintaining the code base.
	c2.com /cgi/wiki?AbstractStaticVariables (873 words)

	Abstract Classes (Site not responding. Last check: 2007-10-20)
		Once again, in many ways abstract classes are a simple concept (involving only one new keyword that can be used in two places) that has deep ramifications when designing complex class hierarchies.
		Sometimes a class should define a method that logically belongs in the class, but that class cannot specify how to implement the method.
		Generally, "Classes should be closed for modification but open for extension." This means that once the specification and implementation of a class stabilizes, we should never change it; instead we can extend it with subclasses that behave similarly but not identically, if we need different state and behavior.
	www.cs.cmu.edu /~pattis/15-1XX/15-200/lectures/abstractclasses/lecture.html (4555 words)

	Pattern Summaries: Abstract Factory Pattern
		Classes in the Client role use various widget classes to request or receive services from the product that the client is working with.
		Client classes that call these methods should not have any direct knowledge of these concrete factory classes, but instead access singleton instances of these classes by calling a method of their abstract factory superclass.
		In that case, the abstract factory class will typically have a static variable set to the concrete factory class that is used for the duration of the program run.
	www.developer.com /java/other/article.php/626001 (1735 words)

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