Question

Need help figuring out what would be the all 12 days output

public class Date {
   private int day;
   private int month;
   private int year;
  
   private static int tracker;
  
   public Date()
   {
       this(1, 1, 2000);
       System.out.println("4");
   }
  
   public Date(int year)
   {
       this(1, 1, year);
       System.out.println("3");
   }
  
   public Date(int month, int year)
   {
       this(1, month, year);
       System.out.println("2");
   }
  
   public Date(int day, int month, int year)
   {
       setDate ( day, month, year);
       tracker ++;
   }
  
   public Date(Date r)
   {
       this(r.day, r.month, r.year);
       System.out.println("1");
   }
  
   public void setDate (int day, int month, int year)
   {
       setMonth(month);
       setDay(day);
       setYear(year);
   }
  
   public void setDay(int day)
   {
       int[] daysPerMonth = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31};
      
       this.day = ((day > 0 && day < daysPerMonth[month]) ? day : 1);
   }
  
   public void setMonth(int month)
   {
       this.month = ((month> 0 && month <= 12) ? month : 1);
   }
  
   public void setYear(int year)
   {
       this.year = year;
   }
  
   public static int getTracker ()
   {
       return tracker;
   }
  
   public String toString()
   {
       return String.format("%02d-%02d=%02d", month, day, year !=0 ? year : 2000);
   }

}

-------------------------

public class Q1
{
   public static void main (String [] args)
   {
       System.out.printf("%d\n", Date.getTracker());
      
       Date[] dateList = new Date[12];
      
       dateList[0] = new Date();
       dateList[1] = new Date(2020);
       dateList[2] = new Date(3, 2020);
       dateList[3] = new Date(25, 3, 2020);
       dateList[4] = new Date(35, 35, 2050);
       dateList[5] = new Date(dateList[3]);
      
       System.out.printf("%d\n", dateList[0].getTracker());
      
       for (int i = 0; i< dateList.length; i++)
           System.out.printf("%d\n", dateList[i]);
   }

}

Answer 1

Let’s go through each line in Q1 class to figure out the output.

System.out.printf("%d\n", Date.getTracker());

This will initially print the number of Date objects created. Initially no objects are created, so this will be 0.

Date[] dateList = new Date[12];

This will create an array of 12 Date objects. All elements will initially be null.

dateList[0] = new Date();

This will initialize Date using default constructor, which itself calls the constructor taking day, month and year passing values 1, 1 and 2000 respectively, and then the default constructor will print 4. (System.out.println("4");) The date object will be stored at index 0 in dateList array.

dateList[1] = new Date(2020);

This will initialize Date using constructor taking year value, which itself calls the constructor taking day, month and year passing values 1, 1 and year respectively, and then the constructor will print 3. The date object will be stored at index 1 in dateList array.

dateList[2] = new Date(3, 2020);

This will initialize Date using constructor taking month and year values, which itself calls the constructor taking day, month and year passing values 1, month and year respectively, and then the constructor will print 2. The date object will be stored at index 2 in dateList array.

dateList[3] = new Date(25, 3, 2020);

This will initialize Date using constructor taking day, month and year values, and nothing will be printed. The date object will be stored at index 3 in dateList array.

dateList[4] = new Date(35, 35, 2050);

This will initialize Date using constructor taking day, month and year values, and nothing will be printed.

Note: Since the day and month values are invalid (35 is not a valid day or month), the day and month values will be initialized to 1.

The date object will be stored at index 4 in dateList array.

dateList[5] = new Date(dateList[3]);

This will initialize Date using constructor taking another Date object, which itself calls the constructor taking day, month and year passing values day, month and year values of the passed Date object respectively (here day=25, month=3 and year=2020), and then the constructor will print 1. The date object will be stored at index 5 in dateList array.

System.out.printf("%d\n", dateList[0].getTracker());

This will print 6 as we have created 6 Date objects and assigned to array indices 0 to 5. The rest of the array elements will be null.

for (int i = 0; i < dateList.length; i++)

                                                System.out.printf("%d\n", dateList[i]);

This will go through each element on the dateList array, and try to print each object as an integer (%d is for denoting integer). Since Date objects are not integers, IllegalFormatConversionException exception will be thrown. If we need to print the Date objects as Strings (invoking toString()), we need to use %s instead of %d. So assuming we use %s instead. Then the loop will print:

01-01=2000

01-01=2020

03-01=2020

03-25=2020

01-01=2050

03-25=2020

null

null

null

null

null

null

Here 01-01=2000 is in the format month-day=year as defined by the toString method of Date class.

So the system will output this if we don’t change %d to %s:

0

4

3

2

1

6

Exception in thread "main" java.util.IllegalFormatConversionException: d !=Date

      at java.util.Formatter$FormatSpecifier.failConversion(Unknown Source)

      at java.util.Formatter$FormatSpecifier.printInteger(Unknown Source)

      at java.util.Formatter$FormatSpecifier.print(Unknown Source)

      at java.util.Formatter.format(Unknown Source)

      at java.io.PrintStream.format(Unknown Source)

      at java.io.PrintStream.printf(Unknown Source)

      at Q1.main(Q1.java:19)

And the system will output this if we change %d to %s:

0

4

3

2

1

6

01-01=2000

01-01=2020

03-01=2020

03-25=2020

01-01=2050

03-25=2020

null

null

null

null

null

null

Let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. If not, PLEASE let me know before you rate, I’ll help you fix whatever issues. Thanks