Homeworks
HW2
Halt an entire program.
System.out.println("ERROR message.");
System.exit(0);
Break complicated problems into smaller pieces (methods).
Call to this() or super() must be first statement in constructor.
Code comparison.
// snippet 1
public Date(int month, int day, int year) { + public Date(int month, int day, int year) {
if(!isValidDate(month, day, year)) { | if (isValidDate(month, day, year)) {
System.out.println("ERROR..."); | this.month = month;
System.exit(0); | this.day = day;
} | this.year = year;
this.month = month; | } else {
this.day = day; | System.out.println("ERROR...");
this.year = year; | System.exit(0);
} | }
+ }
// snippet 2
// what to put after if / else ?
public Date(String s) { + public Date(String s) {
String pattern = "([0-9]{1,2})/([0-9]{1,2})/([0-9]{1,4})"; | if (s.matches("(\\d{1,2})\\/(\\d{1,2})\\/(\\d{1,4})")) {
Pattern r = Pattern.compile(pattern); | String[] date = s.split("/");
| int m = Integer.parseInt(date[0]);
Matcher m = r.matcher(s); | int d = Integer.parseInt(date[1]);
if (m.find()) { | int y = Integer.parseInt(date[2]);
this.month = Integer.parseInt(m.group(1)); | if (isValidDate(m, d, y)){
this.day = Integer.parseInt(m.group(2)); | this.month = m;
this.year = Integer.parseInt(m.group(3)); | this.day = d;
| this.year = y;
if (!isValidDate(this.month, this.day, this.year)) { | } else {
System.out.println("ERROR..."); | System.out.println("Error! Not a Valid Date: " + s);
System.exit(0); | System.exit(0);
} | }
} | } else {
else { | System.out.println("Error! Not a Valid Date: " + s);
System.out.println("ERROR: given string not match!"); | System.exit(0);
System.exit(0); | }
} | }
} +
// snippet 3
// leap year is any year divisible by 4, except that a year divisible by 100 is not a leap
// year, except that a year divisible by 400 is a leap year after all.
public static boolean isLeapYear(int year) { + public static boolean isLeapYear(int year) {
if (year % 4 == 0){ | if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {
if (year % 400 == 0) { | return true;
return true; | } else {
} else if (year % 100 != 0) { | return false;
return true; | }
} | }
} |
return false; |
} +
// snippet 4
public boolean isBefore(Date d) { + public boolean isBefore(Date d) {
if (this.year < d.year) { | if (year < d.year) {
return true; | return true;
} else if (this.year > d.year) { | } else if (this.year > d.year) {
return false; | return false;
} else { | }
if (this.month < d.month) { | //same year
return true; | if (month < d.month) {
} else if (this.month > d.month) { | return true;
return false; | } else if (month > d.month) {
} else { | return false;
if (this.day < d.day) { | }
return true; | //same month
} else { | if (this.day < d.day) {
return false; | return true;
} | } else {
} | return false;
} | }
} + }
// snippet 5
public boolean isAfter(Date d) { + public boolean isAfter(Date d) {
if (isSameDay(d)) { | return d.isBefore(this);
return false; | }
} |
else { |
return !isBefore(d); |
} |
} +
// snippet 6
public int difference(Date d) { + public int difference(Date d) {
if (isAfter(d)) { | int diff = this.dayInYear() - d.dayInYear();
// this > d | if (year == d.year) {
if (this.year == d.year) { | return diff;
return this.dayInYear() - d.dayInYear(); | } else if (this.isBefore(d)) {
} | return -differenceCalculator(this, d);
else { | } else {
int diff = 0; | return differenceCalculator(d, this);
diff += isLeapYear(d.year) ? 366 - d.dayInYear() : 365 - d.dayInYear(); | }
for (int i = d.year+1; i < this.year; i++){ | }
diff += isLeapYear(i) ? 366 : 365; |
} | /** Determines the difference in days between a same day in different years.
diff += this.dayInYear(); | * d1 is before d2.
return diff; | * The return value will not be negative.
} | */
} | public int differenceCalculator(Date d1, Date d2) {
else if (isSameDay(d)) { | int days = 0;
return 0; | for (int i=0; i < d2.year - d1.year; i++) {
} | days += new Date(12, 31, d1.year+i).dayInYear();
else { | }
return -d.difference(this); | return days - d1.dayInYear() + d2.dayInYear();
} | }
} +