SCJP Brainteaser (5)

[Valentin Crettaz]

Ok, the next one is easy... Of course, nobody is supposed to write code like that, but it's very likely that one day somewhere you'll get to maintain poorly written code. So it doesn't hurt starting right now

What happens when the following code is compiled and run?

public class New {
private String String = "Hello";

public New(String String) {
String = String;
}

public String toString() {
return String;
}

public static void main (String[] args) {
String String = "Hello World";
New instance = new New(String);
System.out.println(instance);
}
}

As usual, you should try to compile and run the code mentally without using any compilers and JVM.

[Loveen Jain]

Hi,

Output should be "Hello"

Because in the Constructor there is no way that the compiler can distinguish that we are talking about the class member.

So it would assign "Hello World" = "Hello World" i.e. String = String.

And as String is initialized to be "Hello" in its declaration itself.
toString() method will use it as it is and will display "Hello" as the output.

Loveen..
Preparing for SCJP1.5

[Ganesh Pujar]

Hello

[Tuhin Ghosh]

Hello

tx
tuhin

[Harshad Khasnis]

The output should be Hello.

There is no problem regarding using String as variable name, since the String data member we are using is in current NameSpace and the String class is in java.lang.String NameSpace.

and for the constructor it will assign the parameter value to itself.

to assign the parameter value to data member we must use this.String = String.

[Burkhard Hassel]

Hi!

Shading and:
There are no reserved keywords that start with an uppercase letter.
"instance" is also no reserved keyword.


Bu.

[Jae Stryker]

and for the constructor it will assign the parameter value to itself.
[/QB]

Bingo - That's the trick part of the question right there (if you can call it a trick of course).

[Sanjeev Singh]

Though the program has variable shading in main method(by declaring String)but all the trick lies in the constructor,assigning the instance varilable values in its own.
So the output is Hello.

[Valentin Crettaz]

Alright, Good job! Congratulations on spotting that shading thing!

Relevant pointers to the JLS:
8.3.3.2 Example: Hiding of Instance Variables

Thanks to those who participated. Stay tuned...

[Joe San]

Hi Valentin,

Waiting for the next one???

[Priyam Srivastava]

change the line:
String=String
to
this.String=String
the O/P comes "Hello World"
this is because in String=String the compiler takes both the String as local varialble of that function and overwrites the value of Local String variable with the same value...
when local variable and class variable has the same name and "this" is not used to distinguish b/w local and class variable the compiler gives preference to local variable
[ November 07, 2006: Message edited by: Priyam Srivastava ]