Binary Search Tree: Recursive toString

Question

It only prints out one item. It is suppose to print the contents of the tree in ascending order

public String toString()
{
    return toString (_root);
}
private String toString(BSTnode root)
{
    if (root == null)
        return "";
    toString(root._left);
    toString(root._right);
    return root._data.toString();
}

Solution

How do you want to show them?

You need to append the Strings, for example.

private String toString(BSTnode root)
{
    StringBuilder builder = new StringBuilder();
    if (root == null)
        return "";
    builder.append(toString(root._left));
    builder.append(toString(root._right));
    return builder.append(root._data.toString()).toString();
}

or just use a concatenation on strings.

private String toString(BSTnode root)
{
    String result = "";
    if (root == null)
        return "";
    result += toString(root._left);
    result += toString(root._right);
    result += root._data.toString()
    return result;
}

Comments

[Janac Meena]

How would I go about adding a comma after each char in the string? i.e. "a,b,c,d,e,f"