Java ConcurrentSkipListMap.ceilingKey() is a method in the Java ConcurrentSkipListMap class that retrieves the smallest key greater than or equal to the specified key. If no such key exists, it returns null. Introduced in Java 2004 with Java 5, ceilingKey() is useful in concurrent applications requiring sorted key management.

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListMap.html