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How to compare two dates without the use of objects?

/** Reports whether or not date1 comes earlier in time than date2. For example, isEarlierThan("12-01-2015",
"02-15-2017") is true but isEarlierThan("10-11-2016", "10-11-2016") and isEarlierThan("09-09-1967", "02-15-1933")is false.
* /
public static boolean isEarlierThan (String date1, String date2)
{
if(date1.compareTo(date2) > 0) {
return true;
}
else if (date1.compareTo(date2) <= 0) {
return false;
}
else {
return true;
}
}
This code works sometimes but no always. I have ran a tests case and it fails. The following test case is below.
public void testIsEarlierThan ()
{
assertTrue(isEarlierThan("12-01-2015", "02-15-2017"));
assertFalse(isEarlierThan("10-11-2016", "10-11-2016"));
assertFalse(isEarlierThan("09-09-1967", "02-15-1933"));
assertTrue(isEarlierThan("02-14-2017", "02-15-2017"));
}
When I run the test case, only the first two work then it stops at the third one. But I don't understand whats wrong? if the first one works shouldn't the third one work just fine? Thanks in advance!

Answering my own question. And for future reference if anyone has a similar question.
public static boolean isEarlierThan (String date1, String date2)
{
String month1 = date1.substring(0, 2);
String month2 = date2.substring(0, 2);
String day1 = date1.substring(3, 5);
String day2 = date2.substring(3, 5);
String year1 = date1.substring(6, 10);
String year2 = date2.substring(6, 10);
date1 = year1 + month1 + day1; // + month1 + day1
date2 = year2 + month2 + day2; // + month2 + day2
if (date1.compareTo(date2) < 0)
{
return true;
}
else if (date1.compareTo(date2) > 0)
{
return false;
}
else
{
return false;
}
}
Basically I have a method that takes the two dates, takes them apart into a year, a month, and a day. Then puts them back together in a different order so that when I compare them it will print the which true if date1 is before date2 or false if date1 is after or equal to date2.

Constructor not setting values? Get method not working [duplicate]

When I try to run this program, the result is always null, 0 0. Why do the values of monthName, day, and year not show up when the getDay() method is invoked and printed on the screen.
public class Assignment1 {
public static void main(String[] args) {
//creates an array of type Date filled with two LongDate objects
Date [] collectionOfDates = { new LongDate("February",2,1996), new LongDate("February",13,1999) };
// loops through the array and displays output of getDate() for each object
for( int i = 0; i < collectionOfDates.length; i++ ) {
System.out.println( collectionOfDates[i].getDate() );
}
}
}
For your information, the LongDate class is a subclass of the Date class which contains methods editDay() and editYear() along with several others. The LongDate method is listed below.
Any help greatly appreciated, Thanks. Also, feel free to comment if you want more information.
public class LongDate extends Date {
private String monthName;
private int day;
private int year;
public LongDate() {
}
public LongDate(String m, int d, int y) {
super.editday(d);
super.edityear(y);
editMonth(m);
}
public void setDate(String m, int d, int y) {
monthName = m;
day = d;
year = y;
}
public String getDate() {
StringBuilder fullDate = new StringBuilder();
fullDate.append(monthName);
fullDate.append(" ");
fullDate.append(day);
fullDate.append(", ");
fullDate.append(year);
return fullDate.toString();
}
public String getShortDate() {
int month = 0;
if (monthName == "January") {
month = 1;
} else if (monthName == "February") {
month = 2;
} else if (monthName == "March") {
month = 3;
} else if (monthName == "April") {
month = 4;
} else if (monthName == "May") {
month = 5;
} else if (monthName == "June") {
month = 6;
} else if (monthName == "July") {
month = 7;
} else if (monthName == "August") {
month = 8;
} else if (monthName == "September") {
month = 9;
} else if (monthName == "October") {
month = 10;
} else if (monthName == "November") {
month = 11;
} else if (monthName == "December") {
month = 12;
}
StringBuilder shortDate = new StringBuilder();
shortDate.append(month);
shortDate.append("/");
shortDate.append(day);
shortDate.append("/");
shortDate.append(year);
return shortDate.toString();
}
protected String editMonth(String m) {
// asks person to try again if month is not capitalized and spelled properly
if (m != "January" && m != "February" && m != "March" && m != "April" && m != "May" && m != "June" && m != "July" && m != "August" && m != "September" && m != "October" && m != "November" && m != "December") {
m = Input.getString( "Invalid month. Please type the month again." );
return m;
} else
return m;
}
}

There's nothing in the constructor of LongDate which sets the fields (monthName, day, and year) that getDate() reads.
I assume that the Date#editDay() and Date#editYear() functions look similar to LongDate#editMonth(). Note that editMonth() does not assign a value to the monthName field!

You should compare your strings with equals() and not ==. The equals() method compares string values, whereas == compares object references, which is not what you want here. So change:
if (monthName == "January") {
to:
if (monthName.equals("January")) {
and similarly for the other comparisons.

Couple of issues. First:
public LongDate(String m, int d, int y) {
super.day(d);
super.year(y);
editMonth(m);
}
You don't show Date so it is unclear to us what day() and year() are supposed to do, but regardless:
public class LongDate extends Date {
private String monthName;
private int day;
private int year;
...
}
Your declarations of these fields are hiding any similar fields that the base presumably has. In any case, at no point in your constructor are you setting this.day or this.year to anything, and so, of course, they remain at their initial value of 0.
You need to clean up your code a bit. Either refer to the correct day and year, or make sure you are setting and getting the base class' version of those fields instead of redeclaring them in the subclass (again, not sure what your base implementation does).
You may want to have a look at the official tutorial on Inheritance. It's concise and well-written and covers topics like overriding methods, hiding fields, etc. I think it will give you a good starting point for solving your issues here.
And, of course, comparing strings with == here will lead to other issues in the future: How do I compare strings in Java?

Your editMonth method returns a string, instead it should set the month:
monthName = m;
Another option is to keep the editMonth method the same, but in your constructor put:
monthName = editName(m);

Creating Java Program to Return Previous, Current, and Next Day

I am creating a final program for my introductory java programming course and I am in need of some assistance. The current day and the next day values are not correctly printing. I have read over my code again and again but I cannot wrap my head around why this is not running properly. Any help/advice is GREATLY appreciated!
The guidelines I must follow for this program assignment are as follows:
A. Set the day.
B. Print the day.
C. Return the day.
D. Return the next day.
E. Return the previous day.
F. Calculate and return the day by adding certain days to the current day. For example, if the current day is Monday and we add four days, the day to be returned is Friday. Similarly, if today is Tuesday and we add 13 days, the day to be returned is Monday.
G. Add the appropriate constructors.
H. Write the definitions of the methods to implement the operations for the class Day, as defined in A through G.
I. Write a program to test various operations on the class Day.
*EDIT***
This new code I have written works excellent until I set the day as Monday. The issue I am having is within the previousDay method. I'm trying to add an if/else statement but I cannot get it to compile correctly without receive an outOfBounds Exception error. What is a good way to accomplish this in a String array?
The UPDATED CODE I have written in attempt to accomplish this program task:
public class Day {
int index;
static String[] days = {"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"};
public Day(String currentDay)
{
for(int i = 0; i < days.length; i++)
{
if(currentDay.equals(days[i]))
{
index = i;
return;
}
}
System.out.println("Days is invalid");
}
public void printDay()
{
System.out.println("The Day is " + days[index]);
}
public String returnDay()
{
return days[index];
}
public String returnNextDay()
{
return days[(index + 1 )% days.length];
}
public String returnPreviousDay()
{
if (days.length <= 1)
return days[index + 6];
else return days[(index - 1)%days.length];
}
public String whatDayIs(int i)
{
return days[(index + i)%days.length];
}
public static void main(String[] args)
{
Day day = new Day("Mon");
day.printDay();
System.out.println("Return Day: " + day.returnDay());
System.out.println("Next Day: " + day.returnNextDay());
System.out.println("Previous Day: " + day.returnPreviousDay());
System.out.println(day.whatDayIs(7));
}
}
Thank you for your time!
Adam

First of all, use java naming conventions. It makes your code clearer and easier to help.
You have some errors in your code:
public Day setNameDay(String Day) {
Day = Days;
return this;
}
What you do here is saving Days value in method's parameter Day which actually does nothing.
public void nextDay() {
Day++;
if (Day <8)
Day = 1;
setDay(Day);
}
Why setting day to one if it is lower than 8? You should use:
if (Day >8) {
Day = 1;
}

"The current day and the next day values are not correctly printing."
nextDay() has no print statement
public void nextDay()
{
Day++;
if (Day <8)
Day = 1;
setDay(Day);
}
And you actually need to call setDay() before Days has a value;
Day myDay = new Day();
myDay.setDay(1);
myDay.printDay();
And the fact that you have a class Day, and int Day and String Days is totally confusing for anyone who is reading your code. I'm surprised you're even able to follow it. Consider Java naming convention: variable names start with lower case.

Your code is full of problems, problems that stem from a deep non-understanding of Java.
For example, look at this:
public Day setNameDay(String Day) {
Day = Days;
return this;
}
It is not only the naming that is bad.
What do you think this method actually does?
I seriuously suggest you take the course again, and pay attention when topics like parameter passing etc. come up.

You can use the Calendar API with Date.
try below code.
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
public class CameoWebServiceClient {
public enum day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}
public static void main(String[] args) {
// read day
int lDay = 5;
SimpleDateFormat date_format = new SimpleDateFormat("yyyyMMdd");
System.out.println(date_format.format(new Date()));
Calendar cal1 = date_format.getCalendar();
cal1.set(Calendar.DAY_OF_WEEK, lDay);
cal1 = setDay(cal1, lDay);
System.out.println(""+curDay(cal1));
System.out.println(""+nextDay(cal1));
System.out.println(""+prevDay(cal1));
}
public static Calendar setDay(Calendar cal1, int lDay) {
cal1.set(Calendar.DAY_OF_WEEK, (lDay));
return cal1;
}
public static String curDay(Calendar cal1) {
int i = cal1.get(Calendar.DAY_OF_WEEK)-1 ;
i = i < 0 ? 6:i;
return day.values()[i]+"";
}
public static String nextDay(Calendar cal1) {
int i = cal1.get(Calendar.DAY_OF_WEEK);
i = i > 6 ? 0:i;
return day.values()[i]+"";
}
public static String prevDay(Calendar cal1) {
int i = cal1.get(Calendar.DAY_OF_WEEK)-2;
i = i < 0 ? 6:i;
return day.values()[i]+"";
}
}

Try updating your method as:
public String returnPreviousDay() {
return days[(index + days.length - 1) % days.length];
}
Here, instead of moving backwards to 0 index, I moved it forward by n - 1 days to get the previous day.

You are trying to re-invent something that already exists and it is making your life harder.
Simply store the data in a Calendar object. Use dateAdd to add and remove days, read the result.

import java.util.*;
import java.lang.*;
import java.io.*;
class Main {
public static void main(String[] args) {
Day day = new Day();
day.setDay(2);
day.printDay();
day.returnDay1(13);
day.returnDay();
day.nextDay();
day.previousDay(); }}
class Day {
int setday = 0;
int returnday=0;
String x,y;
static String[] days = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
void printDay() {
if(setday < 7) {
System.out.println("The Day is " + days[setday]); }
else
System.out.println("Invalid set of day"); }
void setDay(int dayset) {
setday = dayset; }
void returnDay1(int returnday1) {
returnday = returnday1; }
void returnDay() {
if(setday < 7) {
x = days[(setday + returnday )% days.length];
System.out.println("Return Day after "+String.valueOf(returnday)+ " days is " + x); }
else
System.out.println(" "); }
void nextDay() {
if(setday < 7) {
y = days[(setday + returnday + 1 )% days.length];
System.out.println("Next Day is " + y); }
else
System.out.println(" "); }
void previousDay() {
if(setday < 7) {
y = days[(setday + returnday - 1 )% days.length];
System.out.println("Previous Day is " + y); }
else
System.out.println(" "); } }

Java, Creating a calendar

In my Java class, I have to build a calendar application. I've got it mostly completed, however I need help with a couple of methods. I have commented the parts that I need help with. The code includes three classes and a main called TestCalendar. The functions I need help with are located in the Calendar class, named removeEvent(two of them, taking two different arguments), printEvents, and findEvents. Thanks in advance!
Here is the Date class.
public class Date {
int year, month, day;
//constructor
public Date(int yr, int mth, int dy){
year = yr;
if (yr < 2000 || yr > 2100)
{
System.out.println("Wrong Calander Year");
System.exit(1);
}
month = mth;
if (mth < 1 || mth > 12)
{
System.out.println("Wrong Month");
System.exit(1);
}
day = dy;
if (dy < 1 || dy > 31)
{
System.out.println("Wrong Day");
System.exit(1);
}
}
//accessor methods
public int getYear()
{
return year;
}
public int getMonth()
{
return month;
}
public int getDay()
{
return day;
}
//returns date in correct format
public String toString()
{
return "" + month + "/" + day + "/" + year;
}
}
Here is the Event class
public class Event {
Date date;
int hour;
String activity;
Event(int year, int month, int day, int hour, String activity)
{
if (year < 2000 || year > 2100)
{
System.out.println("Wrong Calander Year");
System.exit(1);
}
if (month < 1 || month > 12)
{
System.out.println("Wrong Month");
System.exit(1);
}
if (day < 1 || day > 31)
{
System.out.println("Wrong Day");
System.exit(1);
}
this.date = new Date(year, month, day);
this.hour = hour;
this.activity = activity;
}
public Date getDate()
{
return date;
}
public int getHour()
{
return hour;
}
public String getActivity()
{
return activity;
}
void setActivity(String newActivity)
{
this.activity = newActivity;
}
public String toString()
{
return "" + date +" " + "#" + hour +":" + " " + activity;
}
public boolean equals(Object obj)
{
if (obj instanceof Event)
{
return true;
}
else return false;
}
}
The Calendar class
public class Calander {
static final int MAXEVENTS = 10;
Event[] events;
int numEvents;
// constructor
public Calander() {
numEvents = 0;
events = new Event[MAXEVENTS];
}
void addEvent(int year, int month, int day, int hour, String activity) {
Event newEvent = new Event(year, month, day, hour, activity);
events[numEvents] = newEvent;
numEvents++;
}
void removeEvent(int year, int month, int day, int hour, String activity) {
{
if (events[numEvents] == null);
numEvents--;
}
}
// instructions say to remove (all) Event objects in the Calendar that are equals to the event argument. Use the equals method from the event class
void removeEvent(Event event) {
//what to put here?
}
// this method needs to print every Event in the associated Calendar that matches the date arguments. Print each on a separate line, using the toString method from the Event class.
void printEvents(int year, int month, int day) { // how to set equality
if (this.events[numEvents] == )
{
// what to put here?
}
}
// same as above but matches the (Date date) arguments
void printEvents(Date date) {
toString();
}
// Return the first Event in the Calendar that has a matching (equals) activity field. If no match is found, you must return a reference type, so return null.
Event findEvent(String activity) {
//what to put here?
return null;
}
void dump() {
for (int i = 0; i < MAXEVENTS; i++)
{
if (events[i] != null)
System.out.println(events[i]);
}
}
}

well, your event class has a method:
public boolean equals(Object obj)
Which, presumably, should return whether or not the passed event is equal to the instance.
So your void removeEvent(Event event) method should look similar to the following:
take note that this is psudo-code and not valid java. you're going to have to flesh out the details on your own.
void removeEvent(Event event)
{
foreach(event e in this.events)
{
if(event.equals(e))
{
// remove e from the events array
}
}
}
The rest of the methods are going to more or less be similar in concept to the first one with 2 varying factorrs:
how you identify a match
what you do with the match

Since this is homework, I don't actually want to do your homework. So as a hint, you want to use (your event).equals(comparing to other event), not "==".

Spotify puzzle Best Before

I'm pretty new to Java and tried the Best Before puzzle from Spotify yesterday. I get the "Wrong Answer" error when I send it in.
Checking for other solutions didn't help and I cant figure out which input gives a wrong answer.
At best you would just tell me which code lead to the wrong answer. I should be able to correct the code myself then.
import java.util.Scanner;
public class Bestbefore {
public static void main(String[] args) {
//Process Input String
Scanner scanner = new Scanner(System.in);
String dateString = scanner.nextLine();
Integer a,b,c;
a=Integer.parseInt(dateString.substring(0,dateString.indexOf("/")));
b=Integer.parseInt(dateString.substring(dateString.indexOf("/")+1,
dateString.lastIndexOf("/")));
c=Integer.parseInt(dateString.substring(dateString.lastIndexOf("/")+1));
int[][] va={ //All possible combinations
{a,b,c},
{a,c,b},
{b,a,c},
{b,c,a},
{c,a,b},
{c,b,a}
};
int i=0;
while (!checkDate(va[i][0], va[i][1], va[i][2])
&& i<5) // get the first valid date combination
i++;
//to prevent OutofBoundsException of the while loop
if (!checkDate(va[i][0], va[i][1], va[i][2]))
i++;
if (i==6)
System.out.println(dateString+" is illegal");
else
{ //compare the rest of the va-Array and save the position of the lowest Date in i
for (int k=i+1;k<6;k++)
if (checkDate(va[k][0], va[k][1], va[k][2]))
{
if (ageOfDate(va[k][0], va[k][1], va[k][2])
< ageOfDate(va[i][0], va[i][1], va[i][2]))
i=k;
}
System.out.println(getDate(va[i][0], va[i][1], va[i][2]));
}
}
public static boolean checkDate(int day,int month, int year)
{
int[] dpm={31,28,31,30,31,31,30,31,30,31,30,31}; //Days per Month
if (year<2000)
year=year+2000;
if((year%4==0 && year%100!=0) || year%400==0)
dpm[1]=29; //Leapyear correction
if (month==0 || month>12)
return false;
else
if (day==0 || day>dpm[month-1])
return false;
else
return true;
}
public static int ageOfDate(int day,int month, int year) //to compare 2 dates
{
return ((year*10000)+(month*100)+day);
}
public static String getDate(int day,int month, int year) //for the Output
{
String smonth = String.valueOf(month);
String sday = String.valueOf(day);
if (year<2000)
year=year+2000;
if (month<10)
smonth="0"+smonth;
if (day<10)
sday="0"+sday;
return (year+"-"+smonth+"-"+sday);
}
}

June has 30 days, August and July both have 31. Your array dpm is initialized in a wrong manner. So here is where you can go wrong: 31/06/20 -> earliest possible is 20-th of June 2031 instead of 31-st of June 2020.
Hope this solves your problem.

Might be that you don't handle negative numbers. -3/5/2012 would be valid. Also, your program does not handle invalid integers gracefully as it will exit with an exception. If I pass "as/5/12" output should be "as/5/12 is illegal".
FYI, the following
while (!checkDate(va[i][0], va[i][1], va[i][2])
&& i<5) // get the first valid date combination
i++;
//to prevent OutofBoundsException of the while loop
if (!checkDate(va[i][0], va[i][1], va[i][2]))
i++;
Could be reduced to
while (i <= 5 && !checkDate(va[i][0], va[i][1], va[i][2]))
i++;