Java For loop counter not working when calling recursive method

Question

I'm trying to traverse a list of objects and print out their properties to an xml file, but due to the need of closure tags I need to recursively traverse the children and print their properties as well before coming back to the top of the stack to write out the highest components closure tag.

It seems however that for-loops and recursion do not play well together in java, as for some bizarre reason when I have a method call itself inside of the for loop, the counter "resets" (essentially the counter variable seems to unassign itself when trying to use the for-loop normally with all 3 arguments) when coming to the next iteration of the loop, causing an infinite loop.

I've tried a number of different approaches, including trying to make the counter a static variable in the classes constructor and substituting in a for-each loop instead, all with similar problems. The closest I've come to finding an answer was the following solution, with passing in and returning the counter into the recursive method:

Adding counter to a loop inside a recursive method - Java

However, while this works for the case above, which consists of just adding to a value, it causes problems in that if I don't adjust the counter, it is now one higher than it needs to be and causes indexOutOfBound exceptions, and if I do subtract the counter and/or assign it to 0 before entering the loop, the return is giving back a 0 even if I explicitly add one to the counter before passing it back.

None of this makes any sense. Here is the basic logic of the code I'm using: if anyone knows what is wrong with this, or knows of any alternative solutions, let me know.

public int write(PrintWriter fromPortalTXTFile, String level, Integer counter){
    ...
    if (children) {
        for(;counter < childrenList.size();) {
            counter++;
            counter = ClassName.get(counter - 1).write(fromPortalTXTFile, level, counter);
        }
    }
    else {
        counter++;
    }

    return counter;
}

EDIT: Here is the entire method code due to various requests. It contains references to different functions and has logic unrelated to the problem I'm having, and I can't go into detail about how every part of this method works. The problem is with the for loop that is entered if the component has children, which I still believe is better illustrated above.

// Writes the information about this BOM component out to the from_portal.txt file
public int write(PrintWriter fromPortalTXTFile, String level, Integer counter) throws Exception {

    //Retrieve the item and revision of the BOM line.  If
    //read access is denied, skip the BOM line.
    Debug.println("PERF: Inside printXMLTag: Reading BOMLine props start");        
    TCComponentItem item = TXDExportAction.getItem(currentComponent);
    TCComponentItemRevision rev = TXDExportAction.getItemRevision(currentComponent);
    //if (item == null || rev == null) {
    //    return null;
    //}
    String itemID = item.getProperty("item_id");
    String revID = rev.getProperty("item_revision_id");

    // Get the pdm_occ_id of the current component
    String pdmOccID = TXDExportAction.getBOMLineProperty(currentComponent, "bl_occurrence_uid");

    // Determine if the item is currently selected in the BOM window
    Boolean isSelected = false;

    //if (selectedComponents.contains(currentComponent)){
    //  isSelected = true;
    //}

    // TODO: See if it is actually needed to get the quantity of packed lines

    //If the user created a single occurrence to represent
    //multiple occurrences, get the quantity
    int n = 1;
    boolean packed = currentComponent.isPacked();
    if (!packed) {
        try {
            //String str = icbl.getProperty("bl_quantity");
            String str = TXDExportAction.getBOMLineProperty(currentComponent, "bl_quantity");
            if (str != null) {
                n = Integer.parseInt(str);
            }
        } catch (NumberFormatException e) {
            //Do nothing
        }
    }

    Debug.println("PERF: Inside printXMLTag: Reading BOMLine props  complete");

    //TODO: See why this is in a loop, and if it is necessary
    XMLStringBuffer buf = new XMLStringBuffer();

    //Loop over the BOM line n times
    for (int count = 0; count < n ; count++) {
        //Build the opening XML entry
        //XMLStringBuffer buf = new XMLStringBuffer();
        buf.startTag(TXDExportAction.BOMLINE);
        buf.appendAttribute(TXDExportAction.ITEM_ID, itemID);
        buf.appendAttribute(TXDExportAction.REV_ID, revID);

        buf.appendAttribute(TXDExportAction.PDM_OCC_ID, pdmOccID);
        buf.appendAttribute(TXDExportAction.ITEM_SELECTED, isSelected);

        // If this is not the lowest level tag, don't put in the slash at the end.
        // If it is, close the tag.
        //TODO: Remove writing of tags, add to the BOMElement.write function.
        //if (closureTags == 0){
        //  buf.endTagBracket();
        //}
        //else{
        //  buf.endTag();

        //  //Handle closure tags for parents
        //    for(int i = 0; i < closureTags; i++){
        //      buf.endTag(BOMLINE);
        //    }
        //}


    }
    buf.endTagBracket();

    // Step 3: write a </bomline> tag at the same level
    fromPortalTXTFile.print(level);
    fromPortalTXTFile.println(buf);
    //buf.endTag(TXDExportAction.BOMLINE);

    if (!childBOMElements.isEmpty()){
        // Step 1: print tag + information
        level = level + "    ";
        // Step 2: for each child, call child.write()
        for (; counter < childBOMElements.size();){
            counter ++;
            //BOMElement nextElement = childBOMElements.get(index);
            counter = childBOMElements.get(counter - 1).write(fromPortalTXTFile, level, counter); 
        }
        // </Bomline> tag
        //fromPortalTXTFile.println(buf.endTag(TXDExportAction.BOMLINE));
    }
    else
    {
        // If no children, close the tag with a leaflet
        //fromPortalTXTFile.println(buf);
        counter++;
        fromPortalTXTFile.print(buf.endTag());
    }


    // For some reason, using a recursive function in a for loop resets the counter of the for loop.
    // The only work-around is to pass the counter back as a return method.
    return counter;
}

You haven't got enough closing braces, for one thing... And are you expecting the incremented counter in the recursive call to propagate to the caller? If so, that's just not going to happen: arguments are passed by value in Java. — Jon Skeet
– Jon Skeet, Commented Mar 10, 2014 at 13:48
He did say basic logic. That said, there are various errors in the presentation, going to ask for an actual code-tested example here. — Gorbles
– Gorbles, Commented Mar 10, 2014 at 13:49
I didn't copy-paste code, I typed up psuedocode to simplify it for people reading it so they didn't have to parse through hundreds of lines of unrelated code. I can tell you the syntax is correct in the file and will correct the example. — Christian Boler
– Christian Boler, Commented Mar 10, 2014 at 13:50
What is in childrenList ? Are you sure you are trying to pass childrenList[counter-1] instead of just counter-1? — Jimmy
– Jimmy, Commented Mar 10, 2014 at 13:54
So, the function call can't be correct, can it? Because childrenList[counter-1] isn't an integer. Something seems to be wrong with the logic. — blalasaadri
– blalasaadri, Commented Mar 10, 2014 at 14:02

Gorbles · Accepted Answer · 2014-03-10 15:20:07Z

1

It's because you're increasing the counter before calling the recursive method (which is why you're needing counter - 1 in the recursive call and completely redundant).

That said the problem you're having is with your general construct. You're passing in counter and defining the loop per value of counter. However child objects aren't guaranteed to have their parent's amount of children. Parent A has 3 children, so you're passing in counter with a value of 0, 1 or 2. However, if Child A only has 1 child itself, then a counter of 1 or 2 are going to cause it to fail (with an IndexOutOfBounds error).

public void write(PrintWriter fromPortalTXTFile, String level) {

    . . . 

    if(children) {
        for(int n = 0; n < childrenList.size(); n++) {
            // you need to pass in the child object, unless 
            // you're controlling it with level
            write(childrenList.get(n), level);
        }
    } else {

        . . .

    }
}

Bear in mind this isn't going to be perfect. I don't have access to your entire code. I don't know what level is doing. I don't know how you're getting childrenList.

But you are vastly overcomplicating things. All you need to do is recurse for each child if children exist.

EDIT: from the comment chain:

You're probably not handling the children of the root document correctly. Either that, or you have an infinite loop as it's restarting the for loop forever (so n will always always 0). You can test this by seeing if level is incrementing (or decrementing) correctly.

As such, the above example is not the whole answer. Dealing with how you handle the child objects is a part of the resolution.

edited Mar 10, 2014 at 15:20

answered Mar 10, 2014 at 14:08

Gorbles

1,16813 silver badges29 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

Christian Boler Over a year ago

This does not work, as stated in the question above. When using the following loop structure: for(int n = 0; n < childrenList.size(); n++) { The variable "i" will go back to being 0 after the first iteration. I do not know why, and it is the problem I am trying to work around.

Gorbles Over a year ago

I don't have access to your entire program. All I can do is point out the issues with your existing logic. Sorry if this doesn't help! -- EDIT: the loop counter shouldn't reset as it only has a local scope. You may have other issues in your code.

Christian Boler Over a year ago

The example code you gave would not work on its own, unless it is some weird issue I'm having outside the method. For some reason for-loop counters break when trying to call a recursive method.

Gorbles Over a year ago

"Bear in mind this isn't going to be perfect. I don't have access to your entire code. I don't know what level is doing. I don't know how you're getting childrenList." -- this is probably why my code isn't working. Short of you pasting your ENTIRE program code, you need to look at the differences and figure out where the counter is being reset. That's where the problem will be.

Christian Boler Over a year ago

It gets reset at the start of the for-loop, which is behaving odd in general. Any code I have in the loop after the recursion call is not called, and it jumps back to the start of the loop as if it was being called for the first time.

|

Collectives™ on Stack Overflow

Java For loop counter not working when calling recursive method

1 Answer 1

9 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related