import java.sql.Timestamp;
import java.time.Instant;
import java.time.temporal.ChronoUnit;

class Ideone {

    public static void main (String[] args) {
        Timestamp timestamp = Timestamp.from(Instant.now());
        System.out.println(timestamp);
        System.out.println(Timestamp.from(timestamp.toInstant().minus(3 * 7L, ChronoUnit.DAYS)));
    }
}