Java recursion: object is replaced instead of adding a new one

I am trying to add an object inside an object using recursion. My object contains an arrayList and I am trying to add my objects to this arrayList. But instead of adding a new object, my objects are replaced.

My code that does this: This is where the logic for adding an object is executed. But instead, it gets replaced.

private ArrayList<SubChapters> recursiveSubChapters(ReportingTree tree, LinkedHashMap<String, HashMap<String, String>> linkedHashMap, Boolean isSubTree){
SubChapters subChapters = new Subchapters();
ArrayList<SubChapters> alchildUnits = new ArrayList<SubChapters>();
    final String chapterId = linkedHashMap.get(tree.getUnitID()).get("unit_num");       
    final String chapterName= linkedHashMap.get(tree.getUnitID()).get("unit_name");

        if (!isSubTree) {
        final ArrayList<ReportingTree> branches = tree.getBranches();
        if (branches != null) {
            for (ReportingTree subTree: branches) {
                subChapters.setSubChapters(recursiveSubChapters(subTree, linkedHashMap, false));
//This is where the logic of adding an object is being done. But it is being replaced instead.  
        return alchildUnits;


My guess is that I have been messing around somewhere in a loop, but I cannot figure out where I am confused. Thanks in advance for any suggestions or help.

My subChapters class:

public String subChapterID;
public String subChapterName;
public boolean isSubTree= false;
public ArrayList<SubChapters> subChapters;

and getters and setters.


I have coded the same solution to return a string and see the order on the jsp. It works great. I cannot apply the same to my problem here.

private String recursive(ReportingTree tree, LinkedHashMap<String, HashMap<String, String>> listUnitInfo, boolean isTop) {
                    final String unitID = tree.getUnitID();
                    final HashMap<String, String> unit = listUnitInfo.get(unitID);
                    String output = "";
                    if (!isTop) {
                        output += "<li><a href=\"./" + unitID + "\">" + unit.get("unit_num") + "/" + unit.get("unit_name") + "</a>";
                    final ArrayList<ReportingTree> branches = tree.getBranches();
                    if (branches != null) {
                        if (isTop) {
                            output += "<li><a href=\"./" + unitID + "\">" + unit.get("unit_num") + "/" + unit.get("unit_name") + "</a>";
                        output += "<ul>\n";
                        for (ReportingTree subTree : branches) {
                            output += recursive(subTree, listUnitInfo, false);
                        output += "</ul>";
                    } else {
                        if (isTop) {
                            output += "<li>No units match your criteria.";
                    output += "</li>\n";
                    return output;



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1 answer

What you are doing is subChapters.setSubChapters, which I think you are trying to do is subChapters.addSubChapters.

The reason it works with strings is because you are using + = to add a newline to the old string. Doing setSubChapters will be the same as using = with strings.

addSubChapters will be a method that needs to add something to the ArrayList variable inside your subChapters class.



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