jtreg has a local copy of Runtime.Version with this comment:

/* ============================================================================
 *
 * This is a minimally modified copy of Runtime.Version from JDK 11,
 * for the sole purpose of parsing a JDK version string.
 *
 * When jtreg is updated to use JDK 9 or later as a baseline JDK, this code
 * should be replaced with direct use of {@code java.lang.Runtime.Version}.
 *
 * ============================================================================ */

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