JTree - Implementing TreeNode question

[ehudfisher]

Hi,

I'm trying to use a JTree as a UI to a database table (the lazy way - only querying what i need when i need it). For some reason, though I implemented all the methods needed, The JTree only displays the root and nothing else.

creating th JTree:

public class LibraryBrowser extends JFrame
{
	private static final long serialVersionUID = 1L;
	private TreeModel dtm;
	private JTree tree;
	private DBUtil db;
	
        public LibraryBrowser() {
		setDb(new DBUtil(this));
		db.start();
		dtm = new DefaultTreeModel(getRoot(), true);
		tree = new JTree(dtm);
		add(new JScrollPane(tree));
        }

	private LibEntity getRoot() {
		return db.getTop();
	}

The class that implements TreeNode:

public class LibEntity implements TreeNode{
 
	private static final long serialVersionUID = 1L;
	private Integer id = null;
    private Integer parentId = null;
    private String Title = null;
    private Double Max = null;
    private Double Min = null;
    private String Comment;
    private LibraryBrowser lb;
    private LibEntity parent;
    private List<LibEntity> children = new ArrayList<LibEntity>();
    //private DefaultMutableTreeNode treeNode;

    public LibEntity(LibraryBrowser lb, Integer id, Integer parentID, 
    				 String Title, String Comment, Double Min, Double Max) {
    	super();
    	this.lb = lb;
    	this.id = id;
    	this.parentId = parentID;
    	this.Title = Title;
    	this.Comment = Comment;
    	this.Min = Min;
    	this.Max = Max;
    }
 
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        LibEntity libEntity = (LibEntity) o;

        if (id != null ? !id.equals(libEntity.id) : libEntity.id != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        return id != null ? id.hashCode() : 0;
    }

    @Override
    public String toString() {
        return Title;
    }

	private void getChildrenFromDb() {
		children = lb.getDb().getChildren(id);
		for (LibEntity e : children)
			e.setParent(this);
	}
	
	@Override
	public Enumeration children() {
		System.out.print("children ");
		if (children==null) getChildrenFromDb();
		Vector<TreeNode> vec = new Vector<TreeNode>();
		for(LibEntity ent : getChildren()){
			vec.add(ent);
		}
		return vec.elements();
	}
	
	@Override
	public TreeNode getParent(){
		System.out.print("parent ");	
		return parent;
	}
		
	@Override
	public boolean getAllowsChildren() {
		System.out.print("allowschildren ");
		return !isLeaf();
	}
	
	@Override
	public boolean isLeaf() {
		System.out.print("isleaf ");
		return ((Min>=0) ||(Max>=0));
	}

	@Override
	public TreeNode getChildAt(int childIndex) {
		System.out.print("getChildAt ");
		return children.get(childIndex);
	}

	@Override
	public int getChildCount() {
		return children.size();
	}

	@Override
	public int getIndex(TreeNode node) {
		System.out.print("getIndex ");
		return children.indexOf(node);
	}
}

Assuming the database logic works (it does) - what am I doing wrong?

[DarrylBurke]

'children' is never null, so 'getChildrenFromDb()' is never invoked.

db

[ehudfisher]

Well.. that wasn't the problem (It is a problem, just one that I noticed and solved, just pasted an older version of the code..).

The real problem was that the implementation of getChildCount, is called before "children()", and therefore worked on a null "children" version. I did not see that, because somehow I forgot to put there the debug print that I put in the rest of the overriden methods.

Thanks!