Enthuware

The question:
"Which of the following options would be a valid implementation of tester() method?"

I think the following two methods are perfectly valid:
2.public int tester(){         return 0;     }
and
4.public String tester(){         return "false";     }

Now, to put them in the switch it is not so good. But otherwise they seem to be perfectly valid implementations of the "tester()" method.

Maybe the question should be changed to something in the likes of "What implementation of the tester method is valid for the code to compile".

/Chrilos

Unless explicitly specified, you need to assume that the objective is to provide an answer that will compile.

HTH,
Paul.

Although I answered correctly, I don't really understand one thing.
The code will not compile because of "unreachable statement". This is clear.

But why is this code compile without error? Why compiler can't determine that the return value of tester() method is constant?

That is how the language designers designed it. Return value of a method call is not considered at compile time.

Is boolean and Boolean one of the same thing? Since Java is case sensitive , and int and Int are considered different?

So how come these two are same?

boolean and Boolean are different. Int is not a standard java class and has nothing to do with int.
You should read about wrapper classes in java from a good book. Here is a start: http://www.javatpoint.com/wrapper-class-in-java