hw2打卡

这周总算还是完成任务了hhh

运行代码:

package hw2;
/* Date.java */

import java.io.*;

public class Date {
   private int month;
   private int day;
   private int year;
  /** Constructs a date with the given month, day and year.   If the date is
   *  not valid, the entire program will halt with an error message.
   *  @param month is a month, numbered in the range 1...12.
   *  @param day is between 1 and the number of days in the given month.
   *  @param year is the year in question, with no digits omitted.
   */
  public Date(int month, int day, int year) {
      if(isValidDate(month,day,year)){
          this.month=month;
          this.day=day;
          this.year=year;
      }
      else     
          System.exit(0); 
  }
  /** Constructs a Date object corresponding to the given string.
   *  @param s should be a string of the form "month/day/year" where month must
   *  be one or two digits, day must be one or two digits, and year must be
   *  between 1 and 4 digits.  If s does not match these requirements or is not
   *  a valid date, the program halts with an error message.
   */
  public Date(String s) {
      if(s.matches("\d{1,2}\/\d{1,2}\/\d{1,4}")){
          String[]a=s.split("/");
          month=Integer.parseInt(a[0]);
          day=Integer.parseInt(a[1]);
          year=Integer.parseInt(a[2]);
      }else 
      System.exit(0);
  }

  /** Checks whether the given year is a leap year.
   *  @return true if and only if the input year is a leap year.
   */
  public static boolean isLeapYear(int year) {
      if((year%4==0&&year%100!=0)||(year%400==0)) {
      return true; }
      else return false;
  }

  /** Returns the number of days in a given month.
   *  @param month is a month, numbered in the range 1...12.
   *  @param year is the year in question, with no digits omitted.
   *  @return the number of days in the given month.
   */
  public static int daysInMonth(int month, int year) {
      switch(month) {    
      case 4:case 6:case 9:case 11:
      return 30;
      case 2:if(isLeapYear(year))return 29;else return 28;
      default: 
          return 31;
      }                        
  }

  /** Checks whether the given date is valid.
   *  @return true if and only if month/day/year constitute a valid date.
   *
   *  Years prior to A.D. 1 are NOT valid.
   */
  public static boolean isValidDate(int month, int day, int year) {
     if(year>0&&day<=daysInMonth(month,year)&&month<=12){
     return true;}
     else return false;
  }

  /** Returns a string representation of this date in the form month/day/year.
   *  The month, day, and year are expressed in full as integers; for example,
   *  12/7/2006 or 3/21/407.
   *  @return a String representation of this date.
   */
  public String toString() {
        return(this.month+"/"+this.day+"/"+this.year);         
      }

  /** Determines whether this Date is before the Date d.
   *  @return true if and only if this Date is before d. 
   */
  public boolean isBefore(Date d) {
      if(this.year<d.year)return true;
      else if(this.year==d.year&&this.month<d.month)return true;
      else if(this.year==d.year&&this.month==d.month&&this.day<d.day)return true;
      else return false;
     }
  
  /** Determines whether this Date is after the Date d.
   *  @return true if and only if this Date is after d. 
   */
  public boolean isAfter(Date d) {
      if(isBefore(d)||(this.year==d.year&&this.month==d.month&&this.day==d.day))
           return false;     
      else return true;
                     
  }

  /** Returns the number of this Date in the year.
   *  @return a number n in the range 1...366, inclusive, such that this Date
   *  is the nth day of its year.  (366 is used only for December 31 in a leap
   *  year.)
   */
  public int dayInYear() {
      int num=0;
      for(int i=0;i<this.month;i++)
      num+=daysInMonth(i,this.year);
      num+=this.day;
      return num;                          
  }

  /** Determines the difference in days between d and this Date.  For example,
   *  if this Date is 12/15/2012 and d is 12/14/2012, the difference is 1.
   *  If this Date occurs before d, the result is negative.
   *  @return the difference in days between d and this date.
   */
  public int difference(Date d) {
     if (isAfter(d)) {
      int diff=0;
       for(int i=d.year;i<this.year;i++) {
         if(isLeapYear(i)) diff+=366;
         else diff+=365;}
         int diffday=this.dayInYear()-d.dayInYear();
         return diff+diffday;
     }
     else if (isBefore(d)) {                           // replace this line with your solution
     return -d.difference(this); 
     }
     else return 0;
  } 

  public static void main(String[] argv) {
    System.out.println("
Testing constructors.");
    Date d1 = new Date(1, 1, 1);
    System.out.println("Date should be 1/1/1: " + d1);
    d1 = new Date("2/4/2");
    System.out.println("Date should be 2/4/2: " + d1);
    d1 = new Date("2/29/2000");
    System.out.println("Date should be 2/29/2000: " + d1);
    d1 = new Date("2/29/1904");
    System.out.println("Date should be 2/29/1904: " + d1);

    d1 = new Date(12, 31, 1975);
    System.out.println("Date should be 12/31/1975: " + d1);
    Date d2 = new Date("1/1/1976");
    System.out.println("Date should be 1/1/1976: " + d2);
    Date d3 = new Date("1/2/1976");
    System.out.println("Date should be 1/2/1976: " + d3);

    Date d4 = new Date("2/27/1977");
    Date d5 = new Date("8/31/2110");

    /* I recommend you write code to test the isLeapYear function! */

    System.out.println("
Testing before and after.");
    System.out.println(d2 + " after " + d1 + " should be true: " + 
                       d2.isAfter(d1));
    System.out.println(d3 + " after " + d2 + " should be true: " + 
                       d3.isAfter(d2));
    System.out.println(d1 + " after " + d1 + " should be false: " + 
                       d1.isAfter(d1));
    System.out.println(d1 + " after " + d2 + " should be false: " + 
                       d1.isAfter(d2));
    System.out.println(d2 + " after " + d3 + " should be false: " + 
                       d2.isAfter(d3));

    System.out.println(d1 + " before " + d2 + " should be true: " + 
                       d1.isBefore(d2));
    System.out.println(d2 + " before " + d3 + " should be true: " + 
                       d2.isBefore(d3));
    System.out.println(d1 + " before " + d1 + " should be false: " + 
                       d1.isBefore(d1));
    System.out.println(d2 + " before " + d1 + " should be false: " + 
                       d2.isBefore(d1));
    System.out.println(d3 + " before " + d2 + " should be false: " + 
                       d3.isBefore(d2));

    System.out.println("
Testing difference.");
    System.out.println(d1 + " - " + d1  + " should be 0: " + 
                       d1.difference(d1));
    System.out.println(d2 + " - " + d1  + " should be 1: " + 
                       d2.difference(d1));
    System.out.println(d3 + " - " + d1  + " should be 2: " + 
                       d3.difference(d1));
    System.out.println(d3 + " - " + d4  + " should be -422: " + 
                       d3.difference(d4));
    System.out.println(d5 + " - " + d4  + " should be 48762: " + 
                       d5.difference(d4));
  }
}

运行结果：

程序运行成功之前曾经在一个地方卡了大半天。。。就是在public Date(int month, int day, int year）这个地方，

我之前写的代码

 public Date(int month, int day, int year) {
      if(isValidDate(month,day,year)){
      this.month=month;
          this.day=day;
          this.year=year;
      }
      else     
      System.out.println("Input Error!");      
          System.exit(0); 
  }

也就是在 System.exit(0); 之前加了一行System.out.println("Input error!");想让它显示个错误

结果是这样的，也不会报错，正常运行，但是后面什么都不输出

百思不得其解。。。看到的大神求解答一波~~？