Temporal play, with Friday the 13th example.

NextFriday13th.java

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.time.temporal.TemporalQuery;

import static java.time.DayOfWeek.FRIDAY;
import static java.time.temporal.ChronoField.DAY_OF_MONTH;

/**
 * <p>
 * For the next Friday the 13th:
 * </p>
 * <ul>
 *    <li>{@link DateTimeFormatter}</li>
 *    <li>{@link TemporalQuery}</li>
 *    <li>{@link LocalDateTime}</li>
 *    <li>{@link ZoneId}</li>
 *    <li>{@link OffsetDateTime}</li>
 *    <li>{@link ZoneOffset}</li>
 *    <li>{@link Duration}</li>
 * </ul>
 * <p>
 *     Initial output on 13th of January, 2017:
 *
<pre>Lucky bastard, today is already Friday 13th of January (2017).
Next upcoming lucky day is Friday 13th of October (2017).
For that the wait is approximately 272.25937500000003 days.</pre>
 * </p>
 *
 * @author Taimo Peelo
 */
public class NextFriday13th {
    private static final DateTimeFormatter FORMATTER =
        DateTimeFormatter.ofPattern("eeee dd'th' 'of' MMMM (yyyy)");

    private static final TemporalQuery<Boolean> isFridayThe13th =
        t -> (13 == t.get(DAY_OF_MONTH)) && (FRIDAY == DayOfWeek.from(t));

    public static void main(String[] args) {
        //
        // Maybe its already here?
        //
        LocalDateTime now = LocalDateTime.now();
        if (now.query(isFridayThe13th)) {
            System.out.println("Lucky bastard, today is already "  + FORMATTER.format(now) + ".");
        }

        //
        // When will it be next, then?
        //

        ZoneId systemZO = ZoneOffset.systemDefault();
        OffsetDateTime offsetNow = now.atOffset(systemZO.getRules().getOffset(now));
        OffsetDateTime upcoming = offsetNow.truncatedTo(ChronoUnit.DAYS).plus(1, ChronoUnit.DAYS);

        while (!upcoming.query(isFridayThe13th))
            upcoming = upcoming.plus(1, ChronoUnit.HALF_DAYS);

        System.out.println("Next upcoming lucky day is " + FORMATTER.format(upcoming)  + ".");

        //
        // But how long until the lucky day?
        //

        Duration waitingTime = Duration.between(offsetNow, upcoming);
        BigDecimal approxDaysToWait =
            new BigDecimal(waitingTime.get(ChronoUnit.SECONDS))
                .divide(BigDecimal.valueOf(3600*24), 2, RoundingMode.HALF_UP) ;

        System.out.println("For that the wait is approximately " + approxDaysToWait + " days.");
    }
}