public void toStringBuilder(StringBuilder sb) {
if (!isLeaf()) sb.append('(');
if (getLabel() != null) {
sb.append(getLabel());
}
if (!isLeaf()) {
for (Tree<L> child : getChildren()) {
sb.append(' ');
child.toStringBuilder(sb);
}
sb.append(')');
}
}
/* Returns a string representation of this tree using bracket
* notation. */
public String toString() {
StringBuilder sb = new StringBuilder();
toStringBuilder(sb);
return sb.toString();
}