override Question about abstract class.

[Gong James]

You are creating a ToolBase class which will be extended
by other programmers. The ToolBase class contains a
single abstract method, createTool.
Which of the following statements are true?
a. The ToolBase class must be declared abstract.
b. Classes extending ToolBase must not be declared
abstract.
c. The ToolBase class must not be declared final.
d. The following variable declaration is illegal in any
context "ToolBase myTB;"

concern the question I think the ToolBase must be
declare abstract (because it has a abatract method).as a
result it could not be instance ,so ToolBase myTB
(which mean to ToolBase myTB=new ToolBae() will
compile error.
my ans :a,c;
but given ans: acd
somebody correct me if I am wrong.
Good regard.

[Ragu Sivaraman]

Originally posted by Gong James:
You are creating a ToolBase class which will be extended
by other programmers. The ToolBase class contains a
single abstract method, createTool.
Which of the following statements are true?
a. The ToolBase class must be declared abstract.
b. Classes extending ToolBase must not be declared
abstract.
c. The ToolBase class must not be declared final.
d. The following variable declaration is illegal in any
context "ToolBase myTB;"

concern the question I think the ToolBase must be
declare abstract (because it has a abatract method).as a
result it could not be instance ,so ToolBase myTB
(which mean to ToolBase myTB=new ToolBae() will
compile error.
my ans :a,c;
but given ans: acd
somebody correct me if I am wrong.
Good regard.

Yeah the answer is a,c,d
Abstract class can have its own reference
They do even have constructors( component())
But they cant be instantiated though
Many times you see abstract class being parent and
it is legitimate to have a reference of parent class referring to this concerete subclass
Ragu

[R K Singh]

correct ans are:
a,c
d can not be correct as it says:
it is illegal to ...........
ToolBax tb;
But it is legal as you can have reference variable of abstract class.
so the true options are a,c

------------------
Regards
Ravish

[Salamina Daniel]

d. The following variable declaration is illegal in any
context "ToolBase myTB;"
d. it is legal, see below :
------------------------------
public class Verify {
public static void main(String [] args){
ToolBase myTB=new ChildToolBase();
myTB.amethod();
}
}
abstract class ToolBase {
abstract void amethod();
}
class ChildToolBase extends ToolBase {
void amethod(){System.out.println("In ChildToolBase");}
}
So I agree with ravish kumar
Correct answers are a,c
Best regards