Inheritance

[kathukutti]

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!

 

[Oliver Wong]

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

 

[Robert Klemme]

You should clarify whether A inherits from B or B inherits from A.


"&a=c" doesn't make sense in the context of Java.


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

 

[Mark Space]

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...

I assume all this results from not understanding one's homework question.

 

[Owen Jacobson]

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!

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).

 

[Tor Iver Wilhelmsen]

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).