Java-字符串索引越界异常 "String index out of Range"

Question

我是java新手，硬着头皮问我确信是一个愚蠢的问题。我创建了一些方法，只是想在 main 中调用它们。我在 main 方法中的 while 循环中收到错误。编译器说“线程主 java.lang.StringIndexOutOfBoundsException 中的异常:字符串索引超出范围:0 at java.lang.String.charAt(String.java:686) at Project3.main(Project3.java:61)

任何帮助将不胜感激。谢谢。完整代码如下:

import javax.swing.JOptionPane;
import java.util.Scanner;
public class Project3
{
public static void main(String[] args)
{
 int iScore1;  //first variable input by user to calc average
 int iScore2;  //second variable input by user to calc average
 int iScore3;  //third variable input by user to calc average
 double dAverage; //returned average from the three test scores
 char cLetterGrade; //letter grade associated with the average
 double dGPA;  //the GPA associated with the letter grade
 char cIterate = 'Y';  // loop check
 String strAgain;   //string user inputs after being asked to run again

 System.out.print(createWelcomeMessage());


 //pause in program
 pressAnyKey();

 while (cIterate == 'Y')
 {
 //prompt user for test scores
 System.out.print("\n\nPlease enter the first test score: ");
 Scanner keys = new Scanner(System.in);
 iScore1 = keys.nextInt();

 System.out.print("\nPlease enter the second test score: ");
 iScore2 = keys.nextInt();

 System.out.print("\nPlease enter the third test score: ");
 iScore3 = keys.nextInt();

 //calculate average from the three test scores
 dAverage = calcAverage(iScore1, iScore2,iScore3);
 System.out.print("\nThe average of the three scores is: " + dAverage);

 //pause in program
 pressAnyKey();

 //get letter grade associated with the average
 cLetterGrade = getLetterGrade(dAverage);
 System.out.print("\nThe letter grade associated with the average is " + cLetterGrade);

 //pause in program
 pressAnyKey();

 //get the GPA associated with the letter grade
 dPGA = calcGPA(cLetterGrade);
 System.out.print("\nThe GPA associated with the GPA is "+ dGPA);

 //pause in program
 pressAnyKey();

 System.out.print("\nDo you want to run again?(Y or N):_\b");
 strAgain = keys.nextLine;
 strAgain = strAgain.toUpperCase();
 cIterate = strAgain.charAt(0);
 }//end while

 //display ending message to user
 System.out.print(createEndingMessage());

 }//end main method
}//end class Project3

public static String createWelcomeMessage()
{
 String strWelcome;
 strWelcome = "Why hello there!\n";
 return strWelcome;
}//end createWelcomeMessage()

public static String createEndingMessage()
{
 String strSalutation;
 strSalutation = "See you later!\n";
 return strSalutation;
}//end createEndingMessage()

public static void pressAnyKey()
{
 JOptionPane.showMessageDialog(null, "Press any key to continue: ");
}//end pressAnyKey()

public static int getTestSCore()
{
 int iScore;
 System.out.print("Enter a test score: ");
 Scanner keys = new Scanner(System.in);
 iScore = keys.nextInt();
 return iScore;
}//end getTestSCore()

public static int calcAverage(int iNum1, int iNum2, int iNum3)
{
 double dAverage;
 dAverage = ((double)iNum1 + (double)iNum2 + (double)iNum3) / (double)3.0;
 return dAverage;
}//end calcAverage(int iNum1, int iNum2, int iNum3)

public static char getLetterGrade(double dGrade)
{
 char cLetter;

 if (dGrade <60)
 {
  cLetter = 'F';
 }
 else if (dGrade >=60 && dGrade <70)
 {
  cLetter = 'D';
 }
 else if (dGrade >=70 && dGrade <80)
 {
  cLetter = 'C';
 }
 else if (dGrade >=80 && dGrade <90)
 {
  cLetter = 'B';
 }
 else if (dGrade >=90)
 {
  cLetter = 'A';
 }

 return cLetter;
}//end getLetterGrade(double dGrade)

public static double calcGPA(char cLetterGrade)
{
 double dGPA;

 if (cLetterGrade == 'A')
 {
  dGPA = 4.0;
 }
 else if (cLetterGrade == 'B')
 {
  dGPA = 3.0;
 }
 else if (cLetterGrade == 'C')
 {
  dGPA = 2.0;
 }
 else if (cLetterGrade == 'D')
 {
  dGPA = 1.0;
 }
 else
 {
  dGPA = 0.0;
 }
 return dGPA;
}//end calcGPA(char cLetterGrade)

Answer 1

您正在使用 scanner.nextInt() 读取三个整数。由于 nextInt 不会在读取 token 后消耗任何空格或换行符，这意味着如果用户输入数字并按 Enter 键，流中仍然存在换行符。

因此，当您稍后调用 nextLine 时，它只会读取该换行符并返回空字符串。

由于对空字符串调用 charAt 会导致越界错误，因此您会得到这样的错误。

要解决此问题，请使用 next 而不是 nextLine，它将读取下一个单词(消耗其之前的所有空格)，而不是下一行，或者调用nextLine 两次。一次消耗换行符，一次读取实际行。

您仍然应该检查用户是否输入空行。