Nested Classes Test

[Eddie Long]

abstract class A {            // 1
  abstract final void m1();   // 2
  abstract final class B {}   // 3
  class C extends B {}        // 4
}

Which line does not result in a compile-time error?
a. 1
b. 2
c. 3
d. 4
e. None of the above
I would say d but apparently the answer is a. Surely abstract + final is a big no no!?
[ November 17, 2003: Message edited by: Eddie Long ]

[Jessica Sant]

This is one of those tricky worded questions...
Which line does not result in a compile-time error?

abstract class A {            // 1  ok
  abstract final void m1();   // 2  problem: abstract + final
  abstract final class B {}   // 3  problem: abstract + final
  class C extends B {}        // 4  problem: cannot subclass a final class
}

just try running the code to see what the compiler says if you want to double check:

C:\blah>javac A.java
A.java:3: illegal combination of modifiers: abstract and final
  abstract final class B {}   // 3
                 ^
A.java:2: illegal combination of modifiers: abstract and final
  abstract final void m1();   // 2
                      ^
A.java:4: cannot inherit from final A.B
  class C extends B {}        // 4
                  ^
3 errors

[Eddie Long]

Thanks a lot Jess.
Sun's trying to turn me into a walking compiler! otherwise i don't see how spotting that kind of mistake makes you a better Java Programmer

[Anup Agrawal]

When you copile the above code why the error is shown
first in the line 3 and then in line 2 and then in line 4.
Why the error is not in the following order
error in line 2
error in line 3
error in line 4
As compiler compiles the first error it will encounter it should report the first error and then the second error. Then why line 3 is the first error it encountered instead of line 2 error.
Can someone tell me why it is like this?

[Dan Chisholm]

Eddie,
Thank you for using my exam.

Sun's trying to turn me into a walking compiler! otherwise i don't see how spotting that kind of mistake makes you a better Java Programmer

The idea is not to learn how to spot mistakes as well as the compiler. The idea is to learn the proper use of each modifier. A programmer is far more likely to use modifiers effectively when the rules are known. Furthermore, learning the rules will help a programmer write quality code and write it quickly. A programmer that depends on coaching from the compiler is unlikely to be as productive as a programmer that does not need the coaching.
Anup,
I am not an expert on compilers, but I do know that most compilers do the job using multiple passes. I assume that the order of the error messages is influenced by the multiple pass approach to compilation.