Nested for loop inside a while loop - Java

Question

Hello all,

I was working on a Java web application, and had the following requirement with respect to looping in my HTML table.

I've a nested for loop inside a while loop(both execute the same # of times, for ex. say 3).

My code looks something like this:

<table>
<thead>...</thead>
<tbody>

    if (patcases != null && patcases.size() > 0) {
                Iterator itr1 = patcases.iterator();
                while (itr1.hasNext()) {
                    ..some code here..

                    System.out.println("DA Email from webpage..."+da.getEmail());
                       int rCount = 0;  
       <tr>                
                       for(int i=0;i<passedValues.length; i++){

                         ...some code here..
       </tr>

                       System.out.println("Printed row..." +rCount);
                rCount ++;
} /*closing of for loop */
}/*closing of while loop */
}/* closing of if loop */
</tbody>
</table>

Now, with this type of looping structure, I get the following on my console:

DA Email from [email protected]
Printed row...0
Printed row...1
Printed row...2
DA Email from [email protected]
Printed row...0
Printed row...1
Printed row...2
DA Email from [email protected]
Printed row...0
Printed row...1
Printed row...2

But the type of output I wanted was, something as follows:
DA Email from [email protected]
Printed row...0
DA Email from [email protected]
Printed row...1
DA Email from [email protected]
Printed row...2

How would I go about doing this?
Any help would be greatly appreciated.

Answer 1

It looks like you want parallel iteration.

Simply do something like this:

Iterator<?> iter1 = ...;
Iterator<?> iter2 = ...;             // or: int index = 0;

while (iter1.hasNext() &&
           iter2.hasNext()) {        // or: index < MAX

   Object item1 = iter1.next();
   Object item2 = iter2.next();      // or: index++;

   doSomething(item1, item2);        // or: doSomething(item1, index);

}

// perhaps additional handling if one ran out before the other

Note that if at all possible, so you should use parameterized types instead of raw types (Effective Java 2nd Edition, Item 23: Don't use raw types in new code).

Answer 2

It seems to me that you don't want a nested for loop at all. You just want a counter which gets incremented in the while loop:

if (patcases != null && patcases.size() > 0) {
     Iterator itr1 = patcases.iterator();
     int index = 0;
     while (itr1.hasNext()) {
         ..some code here..
         System.out.println("DA Email from webpage..."+da.getEmail());
         if (index < passedValues.length) {
             System.out.println("Printed row..." + index);
         } else {
             // Hmm, didn't expect this...
             // (Throw exception or whatever)
         }
         index++;
     }
     if (index != passedValues.length) {
         // Hmm, didn't expect this...
         // (Throw exception or whatever)
     }
 }

Answer 3

"Nested for loops" doesn't mean "interlaced for loops". For example, saying:

for (i = 0; i < 3; i++) {
    print("i: " + i);

    for (j = 0; j < 3; j++)
        print("\tj: " + j);
}

prints the following:

i: 0
    j: 0
    j: 1
    j: 2
i: 1
    j: 0
    j: 1
    j: 2
i: 2
    j: 0
    j: 1
    j: 2

What you seem to want is:

i: 0
    j: 0
i: 1
    j: 1
i: 2
    j: 2

Instead of nesting for loops, you would just use a separate counter in the same loop:

j = 0;

for (i = 0; i < 3; i++) {
    print("i: " + i);

    print("\tj: " + j);
    j++;
}