Problems with a loop calling data from an ArrayList.

[moriarty]

I'm writing a program built to store, retrieve and sort data for assignments. I've got most of the code down fine, I've got a seperate Assignment class with .get and .set methods, and everything has been working fine, but in my main program, I'm trying to remove an entry. The program seems to just skip over all the code I've got to remove it.

aryAssignments is my ArrayList containing in each node an Assignment object containing a string and number

int temp = 0;
while(temp < (aryAssignments.size() -1)){
if(strName == (aryAssignments.get(temp)).getAssnName()){

aryAssignments.remove(temp);
System.out.println("All instances of \"" + strName + "\" were found and erased.");

}
else{
System.out.println("\"" + strName + "\" was NOT found.");
}
temp++;
}

This is all under a switch which is clearly getting called (I put in a .println("test"); at the very end of that switch option) but it seems to skip over everything straight to the break;

Anyone have any ideas?

Btw, I originally did this with a for loop, but switched to the while just to see if it'd work. I'm pulling out my hair on this one! Everything else is working fine!

I can provide any additional code if you need it, but I don't believe you'll need it, and I just want a good nudge in the right direction.

[moriarty]

Another question while I'm here, is there a way I can "watch" local variables in eclipse while running my main program? It'd sure help in a situation like this instead of including hidden method calls just to view a temporary variable.

[gcalvin]

        if(strName == (aryAssignments.get(temp)).getAssnName()){

Don't use == to compare Strings.

-Gary-

[pbrockway2]

If the body of the while block is not being executed (is this what you mean by "skipping over everything straight to the break"?) then aryAssignments.size() is zero or one.

[moriarty]

Gary: What should I be doing instead of using ==?

pbrock: Yes, the body of the while block isn't being executed, neither the if or else statements.

I'll check and see what aryAssignments.size() is reporting.

[pbrockway2]

If you think the size() should be bigger than 1, then you'll need to go back to wherever you thought it should have got that larger value and see why that didn't happen.

[Edit]

Use someStr.equals(otherStr) for comparing Strings (and other objects).

[Fubarable]

Gary: What should I be doing instead of using ==?

Use either the equals(...) or equalsIgnoreCase(...) method.

[moriarty]

If I add more than 1 element to the ArrayList, it'll shoot out the else ("...not found")

I suspect Gary is right and that I'm comparing the strings incorrectly.

Edit: Thanks Fubarable, I'm using equalsIgnoreCase now, but still getting the same results. I've got enough parentheses in that line to make my head spin >_< I'll go over it closely

[moriarty]

Less than one error, I believe. ><

Working back on it, thanks guys.

EDIT: Yep, that was it. Just removed the -1 in the statement. Go figure, ID10T error on my part. :P

[pbrockway2]

I've got enough parentheses in that line to make my head spin >_<

There's no extra charge for using local variables!

Edit: I'm glad you've got it sorted out.

[moriarty]

There's no extra charge for using local variables!

:D

How can something so infuriating be so intriguing?

...damn you java...

[moriarty]

It doesn't seem to want to remove the node, but at least it's trying to now. I'm going to keep playing with it, if anyone has a suggestion it'd be helpful.

Also, my "not found" line is logically austistic. It displays it every time if it isn't found, there a quick fix for that or should I make a boolean showing if it was found or not?

[gcalvin]

You can remove() either by index or by value, so your code might be easier to understand if you did it this way:

    boolean nameFound = false;
    for (Assignment assignment : aryAssignments) { // I think "assignments" is a better name for the ArrayList, btw
        if (strName.equals(assignment.getAssnName()) {
            aryAssignments.remove(assignment);
            nameFound = true;
        }
    }
    if (nameFound) {
        System.out.println("All instances of \"" + strName + "\" were found and erased.");
    } else {
        System.out.println("\"" + strName + "\" was NOT found.");
    }

EDIT: Sorry, don't try this. Apparently I was misinformed or misunderstood. It is NOT safe to remove elements while doing for-each iteration. More soon.

-Gary-

[moriarty]

					case 2: {//Remove an assignment							
						System.out.println("\nPlease enter the assignment name:");
						String strName = keyboard.next();

						for(int j = 0; j < (aryAssignments.size()); j++){
							if(strName.equalsIgnoreCase((aryAssignments.get(j)).getAssnName())){
								aryAssignments.remove(j);
								System.out.println("All instances of \"" + strName + "\" were found and erased.");
							}
							else{
								System.out.println("\"" + strName + "\" was NOT found.");
							}
							
						}

					break;}

Edit: just saw the last post, i'm going to look over it, but just posting my current code for reference.

[moriarty]

for (Assignment assignment : aryAssignments)

is the only part where I'm a bit lost, I haven't used syntax like that before. Could you explain it?

By the way, you guys are a fantastic help, I'm learning a lot from this error. :P

[gcalvin]

Sorry, looks like I was mistaken. Give me a minute and I'll post more.

-Gary-

[moriarty]

EDIT: Sorry, don't try this. Apparently I was misinformed or misunderstood. It is NOT safe to remove elements while doing for-each iteration. More soon.

-Gary-

Thank Java for comment blocks. :D

also, I got in a habit of putting a short little note of what the varibles type in high school, haven't kicked it :P
ex: intInteger lngLong strString, etc

[gcalvin]

OK, here's how you really want to do it.

    boolean nameFound = false;
    for (Iterator<Assignment> iter = aryAssigments.iterator(); iter.hasNext(); ) { // note empty third part
        if (strName.equals(iter.next().getAssnName()) {
            iter.remove();
            nameFound = true;
        }
    }
    if (nameFound) {
        System.out.println("All instances of \"" + strName + "\" were found and erased.");
    } else {
        System.out.println("\"" + strName + "\" was NOT found.");
    }

Iterator (Java Platform SE 6)

And, for reference,
The For-Each Loop
but you can't use for-each if you're going to be removing elements.

-Gary-

[moriarty]

Hmm, it seems it won't take .getIterator, but I've tried .iterator and .listIterator and it looked like .listIterator worked, but only in the case of 2 objects with identical names.

I'll go over the javadoc

[moriarty]

It seems that it only kicks in if the last element of the ArrayList is what it's looking for, and then it clears the whole array back to a size of 0.