java 为什么在运行此程序时会出现“字符串索引超出范围”错误？
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Why do I get a "String index out of range" error when I run this program?
提问by NEPat10
I am creating a program that converts roman numeral input to it's integer value and every time I run the program I get an error that says,
我正在创建一个程序，将罗马数字输入转换为整数值，每次运行该程序时，我都会收到一个错误消息，
"Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 1
at java.lang.String.charAt(String.java:646)
at romannumeralconverter.RomanNumeralConverter.convert(RomanNumeralConverter.java:20)
at romannumeralconverter.RomanNumeralConverter.romanInput(RomanNumeralConverter.java:68)
at romannumeralconverter.RomanNumeralConverter.printValue(RomanNumeralConverter.java:72)
at romannumeralconverter.RomanNumeralConverter.main(RomanNumeralConverter.java:77)
Java Result: 1"
Now I am new to programming so I don't know what this means exactly. I am guessing my conversion algorithm is wrong in which the roman numeral entered is not read by the loop. Here is what I have:
现在我是编程新手，所以我不知道这到底是什么意思。我猜我的转换算法是错误的，其中输入的罗马数字没有被循环读取。这是我所拥有的：
public class RomanNumeralConverter {
public String getUserInput() {
Scanner numberInput = new Scanner (System.in);
System.out.print("Enter a roman numeral in uppercase: ");
String userInput = numberInput.next();
numberInput.close();
return userInput;
}
public int convert (String userInput) {
int result = 0;
int subtractamount = 0;
int x = userInput.length();
while(x != 0) {
char romanConvert = userInput.charAt(x);
if(x >= 1) {
if(convertChar(romanConvert) >= convertChar(userInput.charAt(x - 1))) {
subtractamount += convertChar(userInput.charAt(x - 1));
}
}
result += convertChar(romanConvert);
x--;
}
result -= subtractamount;
return result;
}
public static char convertChar(char value) {
char result;
switch (value) {
case 'I':
result = 1;
break;
case 'V':
result = 5;
break;
case 'X':
result = 10;
break;
case 'L':
result = 50;
break;
case 'C':
result = 100;
break;
case 'D':
result = 500;
break;
case 'M':
result = 1000;
break;
default:
System.out.println("Invalid character!");
result = 0;
break;
}
return result;
}
public int romanInput() {
return convert(getUserInput());
}
public void printValue() {
System.out.println(romanInput());
}
public static void main (String[] args) {
new RomanNumeralConverter().printValue();
}
}
If my algorithm is wrong, does anyone know how to fix it?
如果我的算法有问题，有人知道如何解决吗？
回答by Bhesh Gurung
You should start with
你应该从
int x = userInput.length() - 1;
The last character in a string is at the index - (length-of-string - 1), not length-of-string.
字符串中的最后一个字符位于索引 - (length-of-string - 1)，而不是 length-of-string。
回答by Ankur Singhal
change userInput.charAt(x);to userInput.charAt(x - 1);
更改userInput.charAt(x);为userInput.charAt(x - 1);
charAt starts with index 0 to length -1
or int x = userInput.length() - 1;
或者 int x = userInput.length() - 1;
@nd issue, everything coming out as 0
@nd 问题，一切都为 0
You are actually using uppercase characters in switch statement.
您实际上是在 switch 语句中使用大写字符。
so just add below statement,in the starting of your function convert(String userInput)
所以只需在函数的开头添加以下语句 convert(String userInput)
userInput = userInput.toUpperCase(); // converts user input to uppercase , even if its is already or not.
code
代码
public int convert(String userInput) {
userInput = userInput.toUpperCase();
int result = 0;
int subtractamount = 0;
int x = userInput.length() - 1;
while (x != 0) {
char romanConvert = userInput.charAt(x);
if (x >= 1) {
if (convertChar(romanConvert) >= convertChar(userInput.charAt(x - 1))) {
subtractamount += convertChar(userInput.charAt(x - 1));
}
}
result += convertChar(romanConvert);
x--;
}
result -= subtractamount;
return result;
}
output
输出
Enter a roman numeral in uppercase: adig
Invalid character!
Invalid character!
Invalid character!
Invalid character!
501
