Problem with isValid() in leap year program

Question

My problem is the method isValid(). I am not supposed to pass anything into the parameters or call any methods beside daysInMonth(). How am I supposed to check if it is a valid day. Here is my code.
public class Date
{private Integer month;     //instance variables
     private Integer day;
     private Integer year;
     private Integer a,b,c;
     public static final int BAD_MONTH = 0;
     public static final int BAD_DAY = 0;
     public static final int BAD_YEAR = 0;
     public Date(int copyMonth, int copyDay, int copyYear)
     {     setMonth(copyMonth);     //calling set methods()
          setDay(copyDay);
          setYear(copyYear);
     }//Date(Integer, Integer, Integer)
     public int getMonth()
          return month;     //returning month
     }//getMonth()
     private void setMonth(int copyMonth)
          if (copyMonth <= 0 || copyMonth > 12)
                    month = BAD_MONTH;
          else
               month = copyMonth;     //setting month
     }//setMonth
     public int getDay()
          return day;     //returning day
     }//getDay()
     private void setDay(int copyDay)
          if (copyDay > 31 || copyDay < 1)
                    day = BAD_DAY;
          else
               day = copyDay;     //setting day
     }//setDay
     public int getYear()
          return year;     //returning year
     }//getYear()
     private void setYear(int copyYear)
          if (copyYear < 0 || copyYear > 9999 || copyYear < 1000)
                    year = BAD_YEAR;
          else
               year = copyYear;     //setting year
     }//setYear
     private String monthName()
          String a;
          int b = getMonth();
          switch(b)
               case 1:
                    a = "January";break;
               case 2:
                    a = "February";break;
               case 3:
                    a = "March";break;
               case 4:
                    a = "April";break;
               case 5:
                    a = "May";break;
               case 6:
                    a = "June";break;
               case 7:
                    a = "July";break;
               case 8:
                    a =  "August";break;
               case 9:
                    a ="September";break;
               case 10:
                    a = "October";break;
               case 11:
                    a = "November";break;
               case 12:
                    a = "December";break;
               default:
                    a ="Month not valid";
          }//switch()
     return a;     //returning month words
     }//monthName()
     private boolean isLeapYear(int in)
          boolean a;
          if(in%4 == 0)
               a = true;
          if(in%100 == 0)
               if(in%400 == 0)
                    a = true;
          a = false;
          else
               a = false;
     return a;
     }//isLeapYear()
     private Integer daysInFebruary(int in)
          if(isLeapYear(in) == true)
               return 29;
          else
               return 28;
     }//daysInFebruary()
     private Integer daysInMonth(int m, int y)
          Integer r;
          if(m == 1)
               r = 31;
          if(m == 2)
               if(isLeapYear(y) == true)
                    r = 29;
               else if (isLeapYear(y) == false)
                    r = 28;
          if(m == 3)
               r = 31;
          if(m == 4)
               r = 30;
          if(m == 5)
               r = 31;
          if(m == 6)
               r = 30;
          if(m == 7)
               r = 31;
          if(m == 8)
               r = 31;
          if(m == 9)
               r = 30;
          if(m == 10)
               r = 31;
          if(m == 11)
               r = 30;
          if(m == 12)
               r = 31;
     return a;
     }//daysInMonth()
     private boolean isValid()
          daysInMonth();
     }//isValid()
     public String toString()
          if (getMonth() == BAD_MONTH || getYear() == BAD_YEAR || getDay() == BAD_DAY)
               return "**Invalid Date**";
          else
               return monthName() + " " + getDay() + ", " + getYear();
     }//toString()
}//Date

Answer 1

Use java.util.GregorianCalendar I think it will have all the tools you need see doc at http://java.sun.com/j2se/1.5.0/docs/api/java/util/GregorianCalendar.html
cheers mait ..