Nested for Loop doubt?

[Joe Harry]

Guys,

Code below,

public class Main  {
 
  public static void main (String[] args) throws Exception {
          int j = 0;
    do for (int i = 0; i++ < 2 ;) 
      System.out.print(i);
    while (j++ < 2);
 }
}

How does the above code compiles? There is no brace for the do loop. Have anyone come across such a loop?? Please explain the logic behind how the complier interprets it?

Thanks in advance.
[ December 07, 2006: Message edited by: Barry Gaunt ]

[Vinayagar Karpagam]

This code will compile only when there is no ; at the end of for loop.

If that is the case, a single statement would do since
no braces are required for the do statement as long as there is only one statement.
But when we put a ; at the end of the for loop, there comes 2 statements for & System.out.print().

Since i could see a smiley in your code, i assumed there could have been a semicolon at the end of for loop.

[Joe Harry]

Vinayagar,

Thanks for the reply.

[Nomula vasudevu]

my answer is it outputs 1 1
if I am wrong correct me. Thanks in advance.

[Burkhard Hassel]

Hi ranchers,

with better indentation the code looks like this:

public class Main {
public static void main(String[] args) {
int j = 0;
do
for (int i = 0; i++ < 2; /* not obligate */ )
System.out.print(i); 
while (j++ < 2);
}
}

prints
121212

No, I've never seen a do loop without braces before. But it just works like a for loop without braces or an if condition without braces. As Vinayagar wrote.


Yours,
Bu.

[ashni Prakash]

Th code works without braces.I have seen many codes without braces.The braces are required to make code readable and clearer.

your code:
-----------------------------------------------------------------

public class Main {
public static void main(String[] args)
{
int j = 0;
do
for (int i = 0; i++ < 2; /* not obligate */ )System.out.print(i);
while (j++ < 2);
}
}
--------------------------------------------------------

the semicolon is needed in the for statement or else it shows compile time error.
The for statement runs two times to every single do-while loop
that is,
when j=0 i=1,i=2
j=1 i=1,i=2
j=2 i=1,i=2

so the output is 121212.

another example without braces

code
------------------------------------------------------------------
if (aNumber >= 0)
if (aNumber == 0) System.out.println("first string");
else System.out.println("second string");
System.out.println("third string");

--------------------------------------------------------------------
code

[Jim Yingst]

I'm a bit surprised to see people say they've never seen braces omitted. Unless you just mean on a do loop, which is maybe understandable because do/while is fairly rare in the first place. But in general, braces may be omitted from any for, while, do, if or else clause, if the body attached to that clause consists of just one statement. In this particular case that's less obvious because the statement a for loop - but note that there's only one line-ending semicolon in that for loop. That's how you can tell that it's just one statement:

for (int i = 0; i++ < 2; /* not obligate */ ) // no semicolon here - statement continues
    System.out.print(i); // semicolon - statement finished

[praks]: The braces are required to make code readable and clearer.

Well, that's a matter of opinion. Some of us view unnecessary braces as line noise. It's true that many people consider it bad form to omit braces in these cases. However I certainly think it's necessary for programmers to be able to read and understand such code, even if they believe code shouldn't be written that way. I don't remember if SCJP intentionally tests on this point - I think it does, but I'm not sure. Regardless, I think any professional Java programmer should understand the language rules well enough to successfully understand why something like this does not work:

for (int i = 0; i < array.length; i++)
    int x = array[i];
    System.out.println("x is: " + x);
System.out.println("done!");

while this does:

for (int i = 0; i < array.length; i++)
    System.out.println("x is: " + array[i]);
System.out.println("done!");

Because at some point in your career, you will probably see examples like both of those.
[ December 07, 2006: Message edited by: Jim Yingst ]

[Burkhard Hassel]

Jim Yingst posted December 07, 2006 12:47 PM

I'm a bit surprised to see people say they've never seen braces omitted.

no, as I said, never saw a do loop without braces.

Bu.

[Jim Yingst]

Ah, point taken.