public interface Metric {}

/** Gauge calculates a specific value at a point in time. */
@Public
public interface Gauge<T> {

    /**
     * Calculates and returns the measured value.
     *
     * @return calculated value
     */
    T getValue();
}

/** A Counter is a metric measured by incrementing and decrementing. */
@Public
public interface Counter extends Metric {

    /** Increment the current count by 1. */
    void inc();

    /**
     * Increment the current count by the given value.
     *
     * @param n value to increment the current count by
     */
    void inc(long n);

    /** Decrement the current count by 1. */
    void dec();

    /**
     * Decrement the current count by the given value.
     *
     * @param n value to decrement the current count by
     */
    void dec(long n);

    /**
     * Returns the current count.
     *
     * @return current count
     */
    long getCount();
}

public class Metrics {

    /** The registry that holds the metrics. */
 	private final MetricRegistry registry;

    /** The metrics reporters container. */
  	private final List<MetricsReporter> reporters;

	/** Register metrics to MetricRegistry. 
 		@param name The name of metric.
		@param metric The metric to register.	
	*/
	public void registerMetrics(String name, Metric metric) {}
}

public class MetricRegistry {

	/** Map of gauge metrics. */
    private final Map<String, Gauge<?>> gauges = new HashMap<>();

    /** Map of counter metrics. */
    private final Map<String, Counter> counters = new HashMap<>();

	/** Register gauge metric. */
 	public void gauge(String name, Gauge gauge) {}

	/** Register counter metric. */
	public void counter(String name, Counter counter) {}
}

public interface MetricsReporter {
	/** Configure reporter after instantiating it.*/
     void open();

    /** Closes this reporter. */
    void close();

	/** Report the current measurements. This method is called periodically by the Metrics. */
	void report();
}

public class CommitMetrics {
	private Metrics metrics;
	private final String COMMIT_DURATION_METRIC = "commitDuration";
	...
	private void registerCommitMetrics(Metrics metrics) {
		metrics.gauge(COMMIT_DURATION_METRIC, new CommitDurationGauge());
	}
	...
}