building tree from a list of nodes

[neetlife]

Hi. There's this tree I need to build, and I'm having problems with it.

I have to read the nodes from a file, which are sorted inorder, and have marker nodes to show where branches end. For example, I have two text files here, with what the trees should look like under them.

nodeA          nodeA
nodeB          nodeB
nodeC          nodeC
endnodeC       endnodeC
nodeD          endnodeB
endnodeD       nodeD
endnodeB       endnodeD
endnodeA       endnodeA
    A              A
    |             / \
    B            B   D
   / \           |
  C   D          C
 

My node class is simply

public class node {
    String s;
    ArrayList<node> children;
    public node(String s) {
        this.s = s;
        children = null;
    }
    //other functions
}
 

As for the tree, I'm having trouble building it.
I read the nodes from the txt file into an ArrayList of nodes. Here's my tree class so far.

//n is the list of nodes read from file
public tree(ArrayList<node> n) {
    //make tree
    root = buildTree(n);
}
 
//return root of new tree
public node buildTree(ArrayList<node> n) {
    node newNode = null;
    while(!n.isEmpty()) {
        String nodeName = n.get(0).toString();
 
        //check if marker node
        if(nodeName.startsWith("end")) return null;
 
        newNode = new node(nodeName);
        n.remove(0);
 
        //recurse
        newNode.addChild(buildTree(n));
    }
    return newNode;
}
 

However, when I run it, root is still null.
I'm wondering if this is even the correct way to go about building this tree. Any advice?

[jkmyoung]

Here's the mistake:
if(nodeName.startsWith("end")) return null;
The first endnode will cascade null down the entire tree.

You want:
if(nodeName.startsWith("end")) {
n.remove(0);
return null;
}