Java add Tree to ArrayList

Question

Im trying to add each node of a Binary Search Tree to an ArrayList in order, I currently have this code...

private ArrayList<String> toArray(TreeNode<Comparable> root)
  {    
    ArrayList<String> array = new ArrayList<String>();
    if(root!= null)
      return null;
    inorder(root.getLeft());
    array.add(root.getValue());
    inorder(root.getRight());
    return array;
  }

but i get this error from running it...

Error: BSTree.java:64: cannot find symbol
symbol  : method add(java.lang.Comparable)
location: class java.util.ArrayList<java.lang.String>

thank you for any help.

This method takes a tree of Comparable:s - there are a lot of Comparable:s that aren't Strings. Only Strings fits into the ArrayList. See? — esej
– esej, Commented May 29, 2015 at 0:16

jatal · Accepted Answer · 2015-05-29 01:09:02Z

1

Would the following Generic method work for you? I'm away from my compiler but solution should be something like this:

  private <T extends Comparable<T>> ArrayList<T> toArray(TreeNode<T> root)
  {    
    if(null == root)
      return null;

    ArrayList<T> array = new ArrayList<T>();
    inorder(root.getLeft());
    array.add(root.getValue());
    inorder(root.getRight());
    return array;
  }

This TreeNode seems similar to the class in this webpage: Some CS Class notes

answered May 29, 2015 at 1:09

jatal

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Comments

Chris · Accepted Answer · 2015-06-06 13:38:07Z

0

I have used something like this

private void inorder(Node u){
            if( tree.isLeaf(u) ){
                arrayList.add(u);
            }else{
                Node v = tree.getLeft(u);
                invorder(v);

                arrayList.add(u);

                v = tree.getRight(v);
                invorder(v);
}

answered Jun 6, 2015 at 13:38

Chris

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