Swatch

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.LinkedHashMap;
import java.util.Map;

public class Swatch {
    private static final Logger log =
            (Logger) LoggerFactory.getLogger(Swatch.class);

    private String msg = null;
    private long startTime = 0;
    private final Map<String, Long> map = new LinkedHashMap<String, Long>();

    public void output() {
        for (final String msg : map.keySet()) {
            log.info("{} in {} ms", new Object[] { msg, map.get(msg) });
        }
    }

    public void start(final String msg) {
        if (startTime != 0) {
            throw new IllegalStateException("Already started");
        }

        startTime = System.nanoTime() / 1000000;
        this.msg = msg;
    }

    public void stop() {
        if (startTime == 0) {
            throw new IllegalStateException("Not started");
        }

        final long now = System.nanoTime() / 1000000;
        Long n = map.get(msg);

        if (n == null) {
            n = 0l;
        }

        n += (now - startTime);

        map.put(msg, n);

        startTime = 0;
        msg = null;
    }
}