public class VersionGenerator {
    private static final AtomicInteger version = new AtomicInteger(0);
    public static int getNextVersion() {
        return version.incrementAndGet();
    }
}

public class HeartBeatState implements Serializable {
    private volatile int generation;
    private volatile int version;
    HeartBeatState(int gen) {
        this(gen, 0);
    }
    public HeartBeatState(int gen, int ver) {
        generation = gen;
        version = ver;
    }

    int getGeneration() { return generation;}
    void updateHeartBeat() { version = VersionGenerator.getNextVersion(); }
    int getHeartBeatVersion() { return version; }
    void forceNewerGenerationUnsafe() { generation += 1; }
    void forceHighestPossibleVersionUnsafe() { version = Integer.MAX_VALUE; }
    public String toString() { return
        String.format("HeartBeat: generation = %d, version = %d", generation, version); }
}