Switch with Boolean ???

[Wolfgang Obi]

Hello,

I am trying to write a switch statement which will check the return statements from 3 called up methods ("february", "century", and "leap")...and based on the boolean values they return to "daysInMonth" certain commands are to be carried out......

is ist possible to use the code segment below the way i have done?
if not, what corrections could i make,....any suggestions?

 publich static void daysInMonth (int year, int month){
 
 february(month);
 century(year);
 leap(year);
 

[B][ S W I T C H  S T A T M E N T  H E R E ??? ][/B]
 
}
 
public static boolean february(int month){

if(month == 02){
return true;
}else return false;
}
 
public static boolean century(int year){

if((year%100)==0){
return true;
}else return false;
}
 
public static boolean leap(int year){

if((year%4) ==0){
return true;
}else return false;
}   
 

[Ernest Friedman-Hill]

"switch" works only with integral types. boolean values have their own branching control structure: the "if" statement.

[Wolfgang Obi]

Hmm,
I'm a bit confused here:

because i was made to understand that if you had several "if statements" following each other you could put them all together into a switch control structure?

so if i have 20 possibilities i would have to put these all into "if statements"?

tahnx!

[Ernest Friedman-Hill]

Booleans have just two values: true and false. Therefore a "boolean switch" could never have more than two branches. To have more than two branches, you'd actually need more than one boolean value -- i.e., you're testing more than one thing. A chain of if... else if... else statements lets you do just that.

[Wolfgang Obi]

okay,
this is what I've decided to do.....how about it?

public static int[] dayGroup   = {28,29,30,31};
 
............
............
 
booleanisLeapCent   = centuryDiv4(year);
booleanisCent       = century(year);
booleanisSchalt     = leap(year);
 
............
............
 
switch (month){
 
 case 1 : days = 31;break;
 
 case 2 : if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)) days = dayGroup[1];
 else days = dayGroup[0];break;
 
 case 3 : days = dayGroup[3];break;
 case 4 : days = dayGroup[2];break;
 case 5 : days = dayGroup[3];break;
 case 6 : days = dayGroup[2];break;
 case 7 : days = dayGroup[3];break;
 case 8 : days = dayGroup[3];break;
 case 9 : days = dayGroup[2];break;
 case 10: days = dayGroup[3];break;
 case 11: days = dayGroup[2];break;
 case 12: days = dayGroup[3];break;
 default: System.out.println("Entry not recognised, please try again!");break;   

[ May 28, 2006: Message edited by: Wolfgang Obi ]
[ May 28, 2006: Message edited by: Wolfgang Obi ]

[Ed Ward]

Wolf-
Just a little switch tip.
If you're going to take the same action for several cases, it is not necessary to explicitly code the action for each case. Just arrange your cases appropriatley.
The following will have the same affect as the switch you coded above.

 
switch (month){
   case 1 : days = 31;break;
   case 2 : if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)) days = dayGroup[1];
 else days = dayGroup[0];break;
 
  case 4 :
 case 6 :
 case 9 :
 case 11: days = dayGroup[2];break;
 
 case 3 :
                 case 5 :
 case 7 :
 case 8 :
 case 10:
 case 12: days = dayGroup[3];break;
 default: System.out.println("Entry not recognised, please try again!");break;

[Chris Wox]

Originally posted by S Root:
Wolf-
Just a little switch tip.
If you're going to take the same action for several cases, it is not necessary to explicitly code the action for each case. Just arrange your cases appropriatley.
The following will have the same affect as the switch you coded above.

 
switch (month){
   case 1 : days = 31;break;
   case 2 : if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)) days = dayGroup[1];
 else days = dayGroup[0];break;
 
  case 4 :
 case 6 :
 case 9 :
 case 11: days = dayGroup[2];break;
 
 case 3 :
                 case 5 :
 case 7 :
 case 8 :
 case 10:
 case 12: days = dayGroup[3];break;
 default: System.out.println("Entry not recognised, please try again!");break;

why don't we have a break after the If condition below
if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)) days = dayGroup[1];


will it not become a fall through case ???

[wise owen]

  case 2 : if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)) days = dayGroup[1]; else days = dayGroup[0];break;

is

  case 2 : 
        if (((isSchalt == true)&&(!(isCent)))||(isLeapCent == true)){
              days = dayGroup[1];
} else {
              days = dayGroup[0];
        }
        break;

.

It is good programming style to always write the curly braces, {}, althought they are not needed if the clause contains only a single statement. The curly braces are a general indicator in Java of a compound statement. This is known as a block of code. (See here)
[ May 29, 2006: Message edited by: wise owen ]

[Campbell Ritchie]

Quicker way to handle February

case FEBRUARY:
   daysInMonth = isLeapYear ? 29 : 28;
   break;    

CR

[Jesper de Jong]

I would do this without a switch statement at all, you can do the whole thing in two lines of code:

public static int[] daysPerMonth = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
 
// ...
 
days = daysPerMonth[month - 1];

[Ernest Friedman-Hill]

Originally posted by Jesper Young:
I would do this without a switch statement at all, you can do the whole thing in two lines of code:

public static int[] daysPerMonth = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
 
// ...
 
days = daysPerMonth[month - 1];

Well, except for the whole leap year thing...

[Jeff Albertson]

This sounds like a job for java.util.Calendar. I whipped up some code, but I'm puzzled by its output:

import java.util.Calendar;
 
public class Test {
    public static void main(String[] args) {
        int year = 2006;
        for (int month = 1; month<= 12; ++month)
            System.out.println(year + "-" + month + " = " + daysInMonth(year, month));
    }
 
    //month parameter is 1 based (1==January)
    public static int daysInMonth (int year, int month){
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, year);
        cal.set(Calendar.MONTH, month-1);
        return cal.getActualMaximum(Calendar.DAY_OF_MONTH);
    }
}

Output:

2006-1 = 31
2006-2 = 31
2006-3 = 31
2006-4 = 30
2006-5 = 31
2006-6 = 30
2006-7 = 31
2006-8 = 31
2006-9 = 30
2006-10 = 31
2006-11 = 30
2006-12 = 31

What's up with February?