这可能是我正在查看的一个简单错误，但是我的问题是，当我尝试返回字符串“ roman”时，它只会返回null。
这是主程序：
/* CCTPG-22 // Assignment 08: Roman Numerals
* @author Kevin R. Trujillo
* @version 10/28/2015
* Purpose: Converts numbers into roman numerals format and vice-a-versa
* Status:
*/
import java.util.*; // For Scanner
public class RomanMain
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
RomanYear year1 = new RomanYear(1975);
RomanYear year2 = new RomanYear(1988);
RomanYear year3 = new RomanYear(2007);
System.out.println(year1.toString());
System.out.println(year2.toString());
System.out.println(year3.toString());
int diff21 = year2.getYearDecimal() - year1.getYearDecimal();
int diff32 = year3.getYearDecimal() - year2.getYearDecimal();
RomanYear y2MinusY1 = new RomanYear(diff21);
RomanYear y3MinusY2 = new RomanYear(diff32);
System.out.println("Year2 minus Year1 is: " + y2MinusY1.getYearRoman());
System.out.println("Year3 minus Year2 is: " + y3MinusY2.getYearRoman());
}
// Add new methods here
} // No code can be here (outside the class)
这是RomanYear类：
/**
* Auto Generated Java Class.
*/
public class RomanYear {
private int decimal ;
private String roman ;
public RomanYear() // default constructor
{
decimal = 0 ;
roman = "" ;
}
public RomanYear(int newYear)
{
decimal = newYear ;
roman = setYearDecimal(decimal);
}
public RomanYear(String newYear )
{
roman = newYear ;
decimal = setYearRoman(roman) ;
}
public int setYearRoman(String roman)
{
String romanNumeral = roman.toUpperCase();
for(int x = 0;x < romanNumeral.length(); x++)
{
char convertToDecimal = roman.charAt(x);
// first step: Easy stuff
switch (convertToDecimal)
{
case 'M': decimal += 1000; break;
case 'D': decimal += 500; break;
case 'C': decimal += 100; break;
case 'L': decimal += 50; break;
case 'X': decimal += 10; break;
case 'V': decimal += 5; break;
case 'I': decimal += 1; break;
}
}
// Now adapt for specials
if (romanNumeral.contains("IV"))
{
decimal-=2;
}
if (romanNumeral.contains("IX"))
{
decimal-=2;
}
if (romanNumeral.contains("XL"))
{
decimal-=20;
}
if (romanNumeral.contains("XC"))
{
decimal-=20;
}
if (romanNumeral.contains("CD"))
{
decimal-=200;
}
if (romanNumeral.contains("CM"))
{
decimal-=200;
}
return decimal ;
}
public String setYearDecimal(int yr)
{
if (decimal > 3999)
{
System.out.println("Decimal Number: " + decimal + " is over 3999. ") ;
System.out.println("Please enter a new number") ;
System.out.println("Program is ending.............") ;
try {
Thread.sleep(2000); //5000 milliseconds is one second.
}
catch(InterruptedException ex) {
Thread.currentThread().interrupt();
}
System.exit(0) ;
}
else
{
int digit;
String roman = "";
// 1000's column
digit = yr/1000;
for (int i = 0; i < digit; i++)
roman = roman + "M";
yr = yr % 1000; // leaves 0 to 999
// 100s column
String [] hunds = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};
digit = yr/100;
roman = roman + hunds[digit];
yr = yr % 100; // leaves 0 to 99
// 10s column
String [] tens = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};
digit = yr/10;
roman = roman + tens[digit];
yr = yr % 10; // leaves 0 to 9
// Ones column
String [] ones = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};
roman = roman + ones[yr];
}
return roman ;
}
public int getYearDecimal()
{
return decimal ;
}
public String getYearRoman()
{
return roman ;
}
public String toString()
{
System.out.print("Decimal: " + decimal + " as Roman Numerals is " ) ;
return roman ;
}
/* ADD YOUR CODE HERE */
}
如果有人可以解释我在做什么错，那将不胜感激，而不仅仅是发布“正确的方法”来做。
谢谢！
最佳答案
在罗马类的顶部，创建一个名为roman的变量。
public class RomanYear {
private int decimal ;
private String roman ;
在setYearDecimal中，创建一个名为roman的新变量。该局部变量隐藏了全局变量。
int digit;
String roman = "";
当您执行
roman = roman + "M";时，您仅更新本地罗马变量。全局变量仍然为空。您需要做的就是从第二个变量前面删除
String。