StringUtils.join(Object[]) performance issue if .toString() is not trivial
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Key: LANG-770
URL: https://issues.apache.org/jira/browse/LANG-770
Project: Commons Lang
Issue Type: Bug
Reporter: Joe Barnett
I have some code that builds syntax trees, and then uses a combination of
TreeNode.toString() and StringUtils.join() to recursively convert that syntax
tree to a String representation.
example .toString() of a SumNode class, where children is a TreeNode[]:
public String toString() {
return StringUtils.join(children, "+");
}
The problem is, StringUtils.join(Object[], String, int, int) is trying to be
too smart about preallocating the StringBuffer size it uses internally, as it
does:
bufSize *= ((array[startIndex] == null ? 16 :
array[startIndex].toString().length())
+ separator.length());
followed by implicitly calling .toString() on each object in the array:
buf.append(array[i]);
For deep syntax trees, this results in incredibly bad performance, as when
traversing the syntax tree, every time we go to the first node, we re-expand
the entire tree below that node (which does the same thing with the first node
below that, etc).
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