I FOUND THE SOLUTION
This code fragment is posting on this site. This code returns the revision which a branch was created from.
final long[] revStart = { -1 };
logClient.doLog(SVNURL.parseURIEncoded(
"https://svn.svnkit.com/repos/svnkit/branches/1.2.x"),
null, SVNRevision.HEAD, SVNRevision.HEAD, SVNRevision.create(1), true,
false, false, 0, null, new ISVNLogEntryHandler() {
public void handleLogEntry(SVNLogEntry logEntry) throws
SVNException {
System.out.println(logEntry);
revStart[0] = logEntry.getRevision();
}
});
System.out.println(revStart[0]);