Java:我需要有关 Date 类的帮助

Question

// Date3.java 
// Date3 class declaration.

public class Date3 
{
   private int month; // 1-12
   private int day; // 1-31 based on month
   private int year; // any year
   private String[] months = new String[]{ "january", "february", "march", "april", "may", "june", "july", "august", "september", "october", "november", "december" }; 


   // constructor: call checkMonth to confirm proper value for month; 
   // call checkDay to confirm proper value for day
   public Date3( int theMonth, int theDay, int theYear )
   {
      month = checkMonth( theMonth ); // validate month
      year = theYear; // could validate year
      day = checkDay( theDay ); // validate day

      System.out.printf( 
         "Date3 object constructor for date %s\n", this );
   } // end Date3 constructor

   public Date3( String m, int d, int y){
       this(m, d, y);
   }

   public Date3( int m, int y){
       this(m,0, y);
   }


   // utility method to confirm proper month value
   private int checkMonth( int testMonth )
   {
      if ( testMonth > 0 && testMonth <= 12 ) // validate month
         return testMonth;
      else // month is invalid 
      { 
         System.out.printf( 
            "Invalid month (%d) set to 1.", testMonth );
         return 1; // maintain object in consistent state
      } // end else
   } // end method checkMonth

   // utility method to confirm proper day value based on month and year
   private int checkDay( int testDay )
   {
      int[] daysPerMonth = 
         { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

      // check if day in range for month
      if ( testDay > 0 && testDay <= daysPerMonth[ month ] )
         return testDay;

      // check for leap year
      if ( month == 2 && testDay == 29 && ( year % 400 == 0 || 
           ( year % 4 == 0 && year % 100 != 0 ) ) )
         return testDay;

      System.out.printf( "Invalid day (%d) set to 1.", testDay );
      return 1;  // maintain object in consistent state
   } // end method checkDay

   public String getMonthString(int month){
        return months[month];
        }


  /* public String monthAsString()
   {
       //returns month as a string rather than an integer
       switch (month)
       {
           case 1: return "January";
           case 2: return "February";
           case 3: return "March";
           case 4: return "April";
           case 5: return "May";
           case 6: return "June";
           case 7: return "July";
           case 8: return "August";
           case 9: return "September";
           case 10: return "October";
           case 11: return "November";
           case 12: return "December";
           default: return "";          
       }         
   }*/




   // return a String of the form month/day/year
   public String toString()
   { 
      return String.format( "%d/%d/%d", month, day, year ); 
   } // end method toString
} // end class Date3





public class Date3Test {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Date3 myDate = new Date3(9, 16, 2011);
        Date3 myDate2 = new Date3("June", 24, 2010);
        Date3 myDate3 = new Date3(259, 2005);

        // all three dates above are equal and will therefore print
        // the same dates

        System.out.println(myDate);
        System.out.println(myDate2);
        System.out.println(myDate3); 

    }

}

Answer 1

我可以理解为什么您提供的模板对于初学者来说可能会有问题:一方面，months-array 不是静态的，另一方面，您的重载构造函数在必须委托(delegate)给 this(int,int,int) 构造函数之前无法访问它。

要修复代码，您必须将月份数组声明为静态，创建一个静态方法将月份字符串转换为月份数字。此外，您必须注释掉特定行才能编译和测试。

那么让我们一起解决 (ii)

替换:

private String[] months 

与:

private static String[] months 

替换:

public Date3( String m, int d, int y){
    this(m, d, y);
}

与:

public Date3( String m, int d, int y){
    this(convMonth(m), d, y);
}
public static int convMonth(String m) {
    int index =1; // january will be 1
    for(String month : months) {
        if(m.equals(month)) break;
        index++;
    }
    return index;
}

像这样注释掉第二个构造函数模板:

/*public Date3( int m, int y){
    this(m,0, y);
}*/

并注释掉对 Date3Test.java 中第二个构造函数模板的调用:

//System.out.println(myDate3); 

现在应该编译并运行并给出 (ii) 的答案。您可以自己解决 (iii)，只需实现注释掉的第二个构造函数模板并重新激活 println()。