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Java Forum / General / June 2007Inheritance
Hi all!!!!!!! consider the following inheritance hierarchy Class A --> Class B --> Class C As per rule: Object of A can be referenced by their subclass objects. Eg: consider a,b,c are objects of classes A,B,C . Here a=b &a=c is applicable but 'object a' can access only its own member nor the members of 'B & C' question: But consider All the classes (A,B,C) override a single method namely disp(). Now case 1: a=b; a.disp();==> calls the Class B's disp() method though it is not a member of A. IIIy for a=c; a.disp() Thanx in advance! > Hi all!!!!!!! > > consider the following inheritance hierarchy > Class A --> Class B --> Class C You should clarify whether A inherits from B or B inherits from A. > As per rule: Object of A can be referenced by their subclass objects. > Eg: consider a,b,c are objects of classes A,B,C . Here a=b &a=c is > applicable but 'object a' can access only its own member nor the > members of 'B & C' "&a=c" doesn't make sense in the context of Java. > question: But consider All the classes (A,B,C) override a single > method namely disp(). Now > case 1: a=b; a.disp();==> calls the Class B's disp() method though it > is not a member of A. > IIIy for a=c; a.disp() I don't see a question here, just a bunch of statements. - Oliver >> Hi all!!!!!!! >> [quoted text clipped - 17 lines] > > I don't see a question here, just a bunch of statements. And I see only "case 1" but no other cases. Also case 1 is already wrong, because first OP states that all override method disp() and then he says it's not member of A. Now what? Weird... robert >> I don't see a question here, just a bunch of statements. > [quoted text clipped - 3 lines] > > Weird... I assume all this results from not understanding one's homework question. > Hi all!!!!!!! > [quoted text clipped - 13 lines] > > Thanx in advance! 1. Ask a question. 2. Show the code, not a description of the code. Simplify it if you need to, but make sure it compiles (or if not, comment the lines which provoke errors from the compiler). På Tue, 05 Jun 2007 15:34:35 +0200, skrev kathukutti <njediscse@gmail.com>: > As per rule: Object of A can be referenced by their subclass objects. > Eg: consider a,b,c are objects of classes A,B,C . Here a=b &a=c is > applicable but 'object a' can access only its own member nor the > members of 'B & C' Correct: The type of the reference a is A, so the compiler only knows about A's methods. > question: But consider All the classes (A,B,C) override a single > method namely disp(). Now > case 1: a=b; a.disp();==> calls the Class B's disp() method though it > is not a member of A. > IIIy for a=c; a.disp() Here you come in contact with virtual methods: The code that is invoked, even though the method signature is looked up in the class A is the code of the actual object's class (B or C). So there you have it: There is a difference between the type of a reference (used by the compiler to restrict what operations can be performed) and the type of the object (used by the runtime to decide which actual operation takes place). Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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