A simple question about inheritance

[Michelle Chang]

    
Drag and Drop
Add methods to the Beta class to make it compile correctly.
class Alpha{
public void bar(int... x){}
public void bar(int x){}
}
public class Beta extends Alpha{
Place here
Place here
Place here
}

Choose three from the followings:
A. private void bar(int x){}
B. public void bar(int x){}
C. public int bar(String x){return 1;}
D. public Alpha bar(int x){}
E. public void bar(int x, int y){}
F. public int bar(int x){return x;}

The answer is BCE

My question is that is that true that because class Beta subclasses Alpha, Beta can either override or overload the methods that Alpha has? Why do D and F cannot fit into that block? Thanks.

[Jim Hoglund]

You may want to check out the method signatures . . . Jim ... ...

[Afzal Rehman]

Hi Michelle,

it's violating the rules of overriding , E is returning Alpha and superclass has void ,
and F is return int and superclass has void.

You need to keep on eye whenever you do override let say..

Must have the same argument List.
Must have the same return type . bu t in java 5 return type can be subclass this
is known as covariant return.
Must not have more restrictive modifier.
May have less less rectrivtive modifier.
etc. checkout..

[Henry Wong]

"Michelle Chang",

Please Quote Your Sources.

Thanks,
Henry

[appu sharma]

  
A. private void bar(int x){} // its not right because it narrow the visibilty of bar
B. public void bar(int x){} // its overriding
C. public int bar(String x){return 1;} //overloading
D. public Alpha bar(int x){} //overrinding method have only covariant return type so in this Alpha is wrong
E. public void bar(int x, int y){} // overloading
F. public int bar(int x){return x;}//here again return type is not covariant    

but in this case void so you cann't return anything..
let us suppose that if there is any method in base class like

   public Alpha bar(){ Alpha A; return A;}
 

then you can write this in your child class this

   public Beta bar(){ Beta B; return B;} 

here Beta is covariant type of Alpha
vinit