I don't think there's any code specifically using the new features introduced in Java 7 (because then it wouldn't be backward compatible and couldn't be used by people running Java 6)
however, the one issue that initially made it incompatible with Java 7 (for people running Java 6 or 5) has been sorted out, in one of the later 4.7 releases.
quoting myself:
http://www.oracle.com/technetwork/java/ ... .html#jdk7Area: API: Utilities
Synopsis: Updated sort behavior for Arrays and Collections may throw an IllegalArgumentException
Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract. The previous implementation silently ignored such a situation.
If the previous behavior is desired, you can use the new system property, java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behavior.
Nature of Incompatibility: behavioral
RFE: 6804124