TreeMap doesn't have specialized implementation for methods putIfAbsent(), computeIfAbsent(), computeIfPresent(), compute(). Default implementation frequently leads to twice tree traversal, that hurts performance.
Suggested implementation improve performance of all 4 operations within 40%-100% (than higher cost of compare operation than more performance boost).
Note: some of these operations are used in new HttpClient (JEP-110, jdk.incubator.httpclient). Performance speedup for HTTP/2 requests are within 5%-15% (depends on size of HTTP headers)