Constructor question

[Bob Vel]

1 class Test {
2 Test(int i) {
3 System.out.println("Creating Rock number "+i);
4 }
5}
6public class SampleConstructor {
7 public static void main(String[] args) {
8 for(int i = 0; i < 10; i++)
9 new Test(i);
10 }
11}
The above code works fine.
If I change line number 9 to Test r = new Test(i);
I am not able to complie code. Why?

[Eric Pramono]

Hi Bob,
That's an interesting one.
I've never tried that one..
Well, apparently the compiler will declare it as "Invalid declaration". You would have to put the curly brackets "()", e.g.:

for (int i=0; i<10; i++) {
    Test r=new Test(i);
}

I've tried with a number of other variable-types' declarations, and it always gave me the same result whenever I miss that curly bracket.
I guess that's how the compiler works. If it sees a variable declaration straight following the for loop then it'll complain, unless we give the curly bracket beforehand.
please anyone, correct my assumption if it's wrong.
- eric

[Bob Vel]

Hi Eric,
Thanks for your reply.
It is not clear yet. How come when you use curly braces it is working fine. I am still confused.

[Eric Pramono]

Hi Bob,
According to JLS 2.2 Grammar Notation
For Statement
for (ForInit; Expression; ForUpdate) Statement
It seems like the variable declaration is not a statement with regards to the compiler.
please also refer to JLS 14.2 Blocks
it seems like LocalVariableDeclarationStatement is a different thing from Statement itself.
please anyone correct me if I'm wrong.
- eric

[Ragu Sivaraman]

We cant declare a variable inside a loop as a single statement.
But we can assign a value to a variable.
If you wanna do both, then they are two different set of
instructions to the compiler. So in the loopbody they become as block of statements. Hence we need a curly braces.
HTH

[Jane Griscti]

JLS §14.2 states that Every local variable declaration statement is immediately contained by a block.
I think the problem, when curly braces are omitted after a <code>for</code> statement, is that the compiler can't tell which block the code belongs to. A <code>for</code> statement implies a block but without curly braces the intention of the statement <code>Test r = new Test(i)</code> isn't clear. Which block does it relate to? The one implied by the <code>for</code> statement or the method block?? The compiler can't tell so it coughs up an error.
Hope that helps.
------------------
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform

[r balasubramanian]

Test r=new Test(i) is not a single statement. It is a block of statement. First we are declaring a variable and then we are assignment a value for the same. Hence, it has to be within the curly braces.
R.Balasubramanian

[Desai Sandeep]

Bob,
The following code snipplet will compile :

<font size=+0><pre>
class Test {
    Test(int i) {
        System.out.println("Creating Rock number "+i);
    }
}
public class SampleConstructor {
    public static void main(String[] args) {
        Test r;
        for(int i = 0; i < 10; i++) {
            r = new Test(i);
        }
    }
}
</pre></font>

In you earlier code snipplet you were doing declaration and initialization together.Since you cannot declare the variable with the same name again, you were getting compile-time error.
Hope this helps,
Sandeep
SCJP2, OCSD(Oracle JDeveloper), OCED(Oracle Internet Platform)

[Bob Vel]

Thank you all for clearing my doubt.

[Kaleem Haqqi]

Dear Bob,
I just complied this code in JDK1.3 compilier. Its works fine and both
new Test(i) & Tesr r =Test(i) complied with no error. Let me know you have JDK 1.3??