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abstract class constructors

preeti khane
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Joined: Mar 12, 2003
Posts: 93
Can an abstract class have constructors?

I would have thought no , as they cannot be instantiated , so there is no real purpose... Am I right?
Marlene Miller
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Joined: Mar 05, 2003
Posts: 1391
Yes, an abstract class can have constructors.
An abstract class may have instance variables and non-abstract methods (common to all concrete subclasses) that operate on those variables. A constructor could be used to initialize the instance variables.
A constructor of a concrete subclass would invoke the superclass constructor to initialize the variables of the abstract superclass.
Marlene Miller
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Joined: Mar 05, 2003
Posts: 1391

Graph is part of a framework. It supplies nearly all of the methods to support a generic graph editor.
SimpleGraph is a client-defined extension that supplies the geometric shapes of the nodes and edges to be used in the graph.

Graph is an abstract class. It needs a constructor to initialize the variables to do its work.

(From Cay Horstmann´┐Żs Object Oriented Design & Patterns)
[ May 27, 2003: Message edited by: Marlene Miller ]
 
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