abstract class

[Anonymous]

Hi!
I found in a mock examn this explanation:
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A class that contains an abstract method must itself be declared as abstract. It may however contain non abstract methods. Any class derived from an abstract class must either define all of the abstract methods or be declared abstract itself.
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Is this true???
Thanks in advance.

[Alex Sbityakov]

Yup.

[Mini Pilla]

Yes,I think it is true.
Thanx
Rajani

[Anonymous]

Then why run whitout error this code??
abstract class Base{
abstract public void myfunc();
public void another(){
System.out.println("Another method");
}
}
public class Abs extends Base{
public static void main(String argv[]){
Abs a = new Abs();
a.amethod();
}
public void myfunc(){
System.out.println("My Func");
}
public void amethod(){
myfunc();
}
}
1) The code will compile and run, printing out the words "My Func"
2) The compiler will complain that the Base class has non abstract methods
3) The code will compile but complain at run time that the Base class has non abstract methods
4) The compiler will complain that the method myfunc in the base class has no body, nobody at all to looove it
The correct answere is 1.

[Anonymous]

Must be Abs abstract class??
thank you.

[norris rath]

Yes the correct answer is 1. The subclass Abs need not be declared as abstract because it provided the implementation for the myfunc()--An abstract method doesn't have a body but the subclass Abs overrides the myfunc()and provides a body. As you can see, the method has two curly braces and some statement in between. When subclass Abs is instantiated, it calls the amethod() and then amethod() calls myfunc() and then the string "My Func" is printed out. If subclass Abs didn't provide the body for the myfunc() then it would have to be declared as Abstract itself or else there is a compiler error. I hope I'm being clear on this. Good luck!
Saki

Originally posted by Jordi Marqu�s:
Then why run whitout error this code??
abstract class Base{
abstract public void myfunc();
public void another(){
System.out.println("Another method");
}
}
public class Abs extends Base{
public static void main(String argv[]){
Abs a = new Abs();
a.amethod();
}
public void myfunc(){
System.out.println("My Func");
}
public void amethod(){
myfunc();
}
}
1) The code will compile and run, printing out the words "My Func"
2) The compiler will complain that the Base class has non abstract methods
3) The code will compile but complain at run time that the Base class has non abstract methods
4) The compiler will complain that the method myfunc in the base class has no body, nobody at all to looove it
The correct answere is 1.

[Mini Pilla]

Yes,the answer is correct.
Abs is not an abstract class because it is implementing all the methods of the Base class.
HTH.
Thanx
Rajani

[Padmaja Balaji]

Hi !
Point-wise clarification :
1) A class that contains an abstract method must itself be declared as abstract.
- Yes. Base class has an abstract method myfunc() and hence it is declared abstract.
2) It may however contain non abstract methods.
- Yes. Base class is having non-abstract method another().
3) Any class derived from an abstract class much either define all of the abstract methods or be declared abstract itself.
- Here, class Abs (which extends Base) defines myfunc() and thus the program compiles fine. In case, Abs doesn't define myfunc(), then Abs has no option but to declare itself as abstract.
Paddy