public static File newFile(File dir) {
        return new File(dir, LEADER_EPOCH_CHECKPOINT_FILENAME);
    }
This class persists a map of (LeaderEpoch => Offsets) to a file (for a certain replica)
<p>
The format in the LeaderEpoch checkpoint file is like this:
-----checkpoint file begin------
0                <- LeaderEpochCheckpointFile.currentVersion
2                <- following entries size
0  1     <- the format is: leader_epoch(int32) start_offset(int64)
1  2
-----checkpoint file end----------
storage/src/main/java/org/apache/kafka/storage/internals/checkpoint/LeaderEpochCheckpointFile.java