Variable might not have been initialized

Question

For my Comp Sci class I have to make a program that finds the number of days in the given month(1-12), do ya'll know why I'm getting the error "variable days might not have been initialized" when trying to return the int "days" from the switch? Here's the code:

public static int getNumberofDays(int month,int year)
   {
      // Imports the required Scanner
      Scanner kbd = new Scanner(System.in);

      final String month;
      final int days;
      switch (month) {
         case 1:  days = 31;
            break;
         case 2:  if ((year % 4 == 0) && year % 100 != 0)
                  {
                     days = 29;
                  }
                  else if ((year % 4 == 0) && (year % 100 == 0) && (year % 400 == 0))
                  {
                     days = 29;
                  }
                  else
                  {
                     days = 28;
                  }
            break;
         case 3:  days = 31;
            break;
         case 4:  days = 30;
            break;
         case 5:  days = 30;
            break;
         case 6:  days = 31;
            break;
         case 7:  days = 31;
            break;
         case 8:  days = 31;
            break;
         case 9:  days = 30;
            break;
         case 10: days = 31;
            break;
         case 11: days = 30;
            break;
         case 12: days = 31;
            break;
         default: month = "invalid";
            break;
      }
      return days;
   }

The code you posted is not accurate. This raises a different compilation error. — Bhesh Gurung, Feb 18 '16 at 15:33
What a tricky question! So many mistakes in one method, very cool! — radoh, Feb 18 '16 at 15:39

score 7 · Answer 1 · edited Jun 20 '20 at 09:12

7

why I'm getting the error "variable days might not have been initialized"

Because:

final int days;

should be:

int days = 0;

Why?

Variables in methods should be initialized
Final variables cannot be modified.

Other errors:

You don't cover all possible values of month in switch
you define a String month, shadowing the parameter int month
The Scanner is unused
many more... XD

My solution using your way

Also, if you don't break a case block next one will be executed, that means you can do:

public static int getNumberofDays(int month,int year) {
    switch (month) {
       case 1:  
       case 3:  
       case 6:  
       case 7:  
       case 8:
       case 10: 
       case 12: 
             days = 31;
          break;
       case 4:
       case 5:
       case 9:
       case 11: 
             days = 30;
          break;
       case 2:  
          if ((year % 4 == 0) && year % 100 != 0)
          {
             days = 29;
          }
          else if ((year % 4 == 0) && (year % 100 == 0) && (year % 400 == 0))
          {
             days = 29;
          }
          else
          {
             days = 28;
          }
          break;
       default: days = -1;
          break;
    }
    return days;
}

My solution: `Calendar`!:

public static int getNumberofDays(int month,int year)
{
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.MONTH, month);
    cal.set(Calendar.YEAR, year);
    return cal.getActualMaximum(Calendar.DAY_OF_MONTH); 
}

Neil solution: `Java-8`

public static int getNumberofDays(int month,int year)
{
    YearMonth yearMonthObject = YearMonth.of(year, month); 
    return yearMonthObject.lengthOfMonth();
}

edited Jun 20 '20 at 09:12

Community

1
1

answered Feb 18 '16 at 15:27

Jordi Castilla

26,609
8
70
109

1

Your repeated assignments are ugly and mean you can no longer use `final`. – Bathsheba Feb 18 '16 at 15:34
@Neil agree, copy paste mistake, modified!! – Jordi Castilla Feb 18 '16 at 15:34
@Bathsheba I dont use final, but agree about repeating statements... my mistake and fixed – Jordi Castilla Feb 18 '16 at 15:35
1

We all missed the fact that `month` is passed as a function parameter. – Bathsheba Feb 18 '16 at 15:38
@Bathsheba I didn't, please read my answer carefully I answer why the error, but also give solutions ignoring declaring variable again – Jordi Castilla Feb 18 '16 at 15:39
But how can you switch on `month`, have integral types as the case labels, then assign `month` to a string in the `default` case? – Bathsheba Feb 18 '16 at 15:40
because I reused OP answer, just updated to `days = -1` – Jordi Castilla Feb 18 '16 at 15:40
@JordiCastilla although your suggestion to use `Calendar` is nice, it's not applicable to OP, since it's his task to write that method... – radoh Feb 18 '16 at 15:41
`int days = 0;` doesn't even look correct. There is no month with 0 days. :) – Bhesh Gurung Feb 18 '16 at 15:42
@BheshGurung please read before comment... – Jordi Castilla Feb 18 '16 at 15:42
I read it, it's helpful for OP. – Bhesh Gurung Feb 18 '16 at 15:43
@radoh How you know OP task cannot be done by using calendar??? also. **His**? are you sure OP is a man? xDDDDD – Jordi Castilla Feb 18 '16 at 15:43
Better still, Java 8's `YearMonth yearMonthObject = YearMonth.of(1999, 2); int daysInMonth = yearMonthObject.lengthOfMonth();` – Neil Feb 18 '16 at 15:43
@JordiCastilla, `For my Comp Sci class I have to make a program ...`, you didn't read OP's question properly – radoh Feb 18 '16 at 15:44
@Neil Java-8 has it's own tag... what does not appear here – Jordi Castilla Feb 18 '16 at 15:44
@radoh and????? you are committed to use plain java in Comp Sci Class??? maybe OP cannot use switch either and must use only if??? – Jordi Castilla Feb 18 '16 at 15:44
The usage of `Calendar` is of no use for OP, he is just getting started with variables. – Bhesh Gurung Feb 18 '16 at 15:45
@BheshGurung this is YOUR GUESS... not OP requirement in question... – Jordi Castilla Feb 18 '16 at 15:45
@JordiCastilla ok, fair enough, I guess it's OP's task to clarify what he can/can't use. – radoh Feb 18 '16 at 15:46
@JordiCastilla So I take that to mean that all versions of Java are valid. Someone stumbling onto this page using Java 8 is probably going to want to copy that huge switch statement into his program and not use the more proper solution. – Neil Feb 18 '16 at 15:46
@Neil agree with that... not `java-8` but `java-7` or `java-6` tags, so all versions are valid! – Jordi Castilla Feb 18 '16 at 15:47
There is a duplicate variable (of different types) in the method, what does that suggest about the OP. – Bhesh Gurung Feb 18 '16 at 15:49
@Neil updated answer with your Java-8 suggestion – Jordi Castilla Feb 18 '16 at 15:50
3

@JordiCastilla Kind of takes the fun out of a homework assignment though, doesn't it? ;) – Neil Feb 18 '16 at 15:52

score 1 · Answer 2 · answered Feb 18 '16 at 15:37

Not all possible paths through your code assign a value to the days variable. Precisely the default block does not.

default: month = "invalid";
           break;

If you change it to

default: month = "invalid";
         days=0
           break;

The warning disappears.

My other questions are:

Why do you define a String month, thus shadowing the parameter month?
Whats the Scanner for?
Why do you assign invalid to month in the default block, you never return it.

Bathsheba · Answer 3 · 2016-02-18T15:35:59.173

0

final String month; is invalid since month is supplied as a parameter to the function.
You don't initialise days on all control paths: The default block in your switch doesn't do it. This is a nice feature of Java as it helps you achieve program stability. There's nothing better than the compiler telling you what to do. Don't force the issue by writing final int days = 0;; instead assign a value to it in the default block.

edited Feb 18 '16 at 15:35

answered Feb 18 '16 at 15:27

Bathsheba

231,907
34
361
483

Especially now I've read the program more carefully – Bathsheba Feb 18 '16 at 15:36
It's worth mentioning that Java 8 now allows you to do simply this to get days of month: `YearMonth yearMonthObject = YearMonth.of(1999, 2); int daysInMonth = yearMonthObject.lengthOfMonth();` – Neil Feb 18 '16 at 15:40
Indeed. I'm assuming (perhaps wildly) that this was a school exercise. – Bathsheba Feb 18 '16 at 15:41
That seems accurate, but god forbid that a professional programmer stumble onto this page and copy that huge switch statement into his program. – Neil Feb 18 '16 at 15:42

mike · Answer 4 · 2016-02-18T15:49:26.910

-2

Add days = 0; to your default case, as such:

default: 
    month = "invalid";
    days = 0;
        break;

You have to give days a value somewhere in the code path before you try to return it. You should also replace final int days; with int days;. Also, you cannot have final String month because month is passed as a parameter to the function.. just remove the redeclaration of month and you're golden.

edited Feb 18 '16 at 15:49

answered Feb 18 '16 at 15:29

mike

455
2
6

It would fix it, but an explanation as to why would be nice. Edit: I take that back, this would only fix one of the two problems. – Neil Feb 18 '16 at 15:35
duh.. I need my morning coffee as well – mike Feb 18 '16 at 15:42
okay okay easy with the downvotes.. savages lol – mike Feb 18 '16 at 15:47

Variable might not have been initialized

4 Answers4

Other errors:

My solution using your way

My solution: Calendar!:

Neil solution: Java-8

My solution: `Calendar`!:

Neil solution: `Java-8`