java.lang.StringIndexOutOfBoundsException : String index out of range Error - Morse to English Java Code

Question

我正在编写摩尔斯电码到英语的 java 代码(如下)，其中 |莫尔斯电码代表字母和数字之间的空格，莫尔斯电码的空格代表2个字母或数字之间。例如，“成为”=“- --- | -...”。摩尔斯电码。

// Import Scanner.
import java.util.Scanner;

public class Project1_szhu1249322
{
    public static void main(String[] args)
    {
    Scanner input = new Scanner (System.in);
    System.out.println("Would you like to translate 'Morse Code' to English, or 'English' to Morse code? (Enter 'Morse Code' or 'English'.)");
    String unit1 = input.nextLine();
    System.out.println("Enter a string of " + unit1 + " characters (for English, numbers and letters, only): ");
    String amountUnit1 = input.nextLine();
    if (unit1.equals("Morse Code"))
        toEnglish(amountUnit1);
    else if (unit1.equals("English"))
        toMorseCode(amountUnit1);
    else
        System.out.println("Invalid data. Enter 'Morse Code' or 'English' without the single quotes.");
}

    public static void toMorseCode(String english)
{
    // Declare variables, arrays, and strings.
    int i = 0;
    int l = english.length();
    int i2 = 2 * i;
    String[] lowerAlphabet = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","1", "2", "3", "4", "5", "6", "7", "8", "9", "0"};
    String[] upperAlphabet = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z","1", "2", "3", "4", "5", "6", "7", "8", "9", "0"};
    String[] morseCode = {".-", "-...", "-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--..",".----","..---","...--","....-",".....","-....","--...","---..","----.","-----"};
    morseCode[i] = lowerAlphabet[i];
    StringBuilder morseBuilder = new StringBuilder();

    // for loops and if statements for result.
    for (i = 0; i < l; i++)
    {
        i2 = 2 * i;
        if (english.charAt(i) != ' ')
            morseBuilder.append(morseCode[i2]);
        else
            morseBuilder.append('|');

        if (morseBuilder.charAt(i - 1) != ' ' && morseBuilder.charAt(i + 1) != 0)
            morseBuilder.append(' ');
    }

    morseCode[i] = upperAlphabet[i];
    // for loops and if statements for result.
    for (i = 0; i < l; i++)
    {
        i2 = 2 * i;
        if (english.charAt(i) != ' ')
            morseBuilder.append(morseCode[i2]);
        else
            morseBuilder.append('|');

        if (morseBuilder.charAt(i - 1) != ' ' && morseBuilder.charAt(i + 1) != 0)
            morseBuilder.append(' ');
    }

    // Display results.
    System.out.println("The corresponding Morse code is " + morseBuilder + ".");
}

public static void toEnglish(String morse)
{
    // Declare variables, arrays, and strings.
    int i = 0;
    int l = morse.length();
    int i2 = i / 2;
    String[] lowerAlphabet = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","1", "2", "3", "4", "5", "6", "7", "8", "9", "0"};
    String[] upperAlphabet = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z","1", "2", "3", "4", "5", "6", "7", "8", "9", "0"};
    String[] morseCode = {".-", "-...","-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--..",".----","..---","...--","....-",".....","-....","--...","---..","----.","-----"};
    morseCode[i] = upperAlphabet[i];
    String english;

    StringBuilder englishBuilder = new StringBuilder();

    // for loops and if statements for result.
    for (i = 0; i < l; i++)
    {
        i2 = i / 2;
        if (morse.charAt(i) == '|')
        {
            englishBuilder.append(' ');
        }
        else
            englishBuilder.append(morseCode[i2]);
    }

    morseCode[i] = lowerAlphabet[i];
    // for loops and if statements for result.
    for (i = 0; i < l; i++)
    {
        i2 = i / 2;
        if (morse.charAt(i) == '|')
        {
            englishBuilder.append(' ');
        }
        else
            englishBuilder.append(morseCode[i2]);
    }

    // Display results.
    System.out.println("The corresponding English is " + englishBuilder + ".");
    }
}

我收到此错误:

Would you like to translate 'Morse Code' to English, or 'English' to Morse code? (Enter 'Morse Code' or 'English'.)
English
Enter a string of English characters (for English, numbers and letters, only): 
to be
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
    at java.lang.AbstractStringBuilder.charAt(AbstractStringBuilder.java:237)
    at java.lang.StringBuilder.charAt(StringBuilder.java:76)
    at Project1_szhu1249322.toMorseCode(Project1_szhu1249322.java:42)
    at Project1_szhu1249322.main(Project1_szhu1249322.java:16)

我不明白为什么它给我这个错误消息。

另外(问题 2)，我应该使用什么 i2 值？ i/2 仅适用于 i(当第一个字符不是空格时。帮助？？？

Answer 1

当i==0时，您在morseBuilder.charAt(i - 1)上失败了