java.lang.StringIndexOutOfBoundsException：字符串索引超出范圍錯誤-莫爾斯語成英語Java代碼

Question

我正在將莫爾斯電碼轉換為英語java代碼（如下），其中| 摩爾斯（Morse）中的空格代表字母和數字之間的空格，摩爾斯（Morse）中的空格代表2個字母或數字之間的空格。 例如，“成為” =“---- | -...”。 在莫爾斯。

// 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 + ".");
    }
}

我收到此錯誤：

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)

我不明白為什么它會給我這個錯誤信息。

另外（ 問題2 ），我應該使用什么i2值？ i / 2僅適用於我（當第一個字符不是空格時。幫助？？？？

Answer 1

當i==0時，您在morseBuilder.charAt(i - 1)上失敗

Answer 2

您的代碼有多個風險點。 當此代碼charAt(i - 1) i=0時，您將獲得異常。 此外，在功能toEnglish完成循環之后，你將有值的i將等於l ，使得下一行morseCode[i] = lowerAlphabet[i]; 如果您的morse字符串的長度> morseCode的長度或lowerAlphabet將導致異常

Answer 3

使用地圖將字母“ A”，“ B”等映射到它們的莫爾斯電碼櫃台，反之亦然，將莫爾斯電碼轉換為英語。 這使您知道在兩者之間進行轉換時要使用的內容。 嘗試以下操作並對其進行修改以適合您的需求。

public static void main(String[] args) throws IOException 
{
    String userInput = "Hello World";
    String converted = ConvertEnglishToMorseCode(userInput);

    System.out.println(userInput + " in Morse Code is " + converted);

    System.out.println(converted + " in English is " + ConvertMorseCodeToEnglish(converted));
} //end main

public static String ConvertMorseCodeToEnglish(String input)
{
    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 = {".-", "-...", "-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--..",".----","..---","...--","....-",".....","-....","--...","---..","----.","-----"};
    HashMap<String, String> morseToEnlgish = new HashMap<>();

    for(int i = 0; i < upperAlphabet.length; i++)
        morseToEnlgish.put(morseCode[i], upperAlphabet[i]);

    String morseToEnglish = "";
    String[] morseSplit = input.split(" ");

    for(int i = 0; i < morseSplit.length; i++)
    {
        morseToEnglish += morseToEnlgish.containsKey(morseSplit[i]) ? morseToEnlgish.get(morseSplit[i]) : " ";
    }

    return morseToEnglish;
}

public static String ConvertEnglishToMorseCode(String input)
{
    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 = {".-", "-...", "-.-.","-..",".","..-.","--.","....","..",".---","-.-",".-..","--","-.","---",".--.","--.-",".-.","...","-","..-","...-",".--","-..-","-.--","--..",".----","..---","...--","....-",".....","-....","--...","---..","----.","-----"};
    HashMap<String, String> englishToMorse = new HashMap<>();

    for(int i = 0; i < upperAlphabet.length; i++)
        englishToMorse.put(upperAlphabet[i], morseCode[i]);

    String[] letters = input.toUpperCase().split("");

    String englishToMorseWord = "";

    for(int i = 0; i < letters.length; i++)
    {
        englishToMorseWord += englishToMorse.containsKey(letters[i]) ? englishToMorse.get(letters[i]) : "|";
        if(i < letters.length - 1)
            englishToMorseWord += " ";
    }

    return englishToMorseWord;
}

產量

Hello World in Morse Code is .... . .-.. .-.. --- | .-- --- .-. .-.. -..
.... . .-.. .-.. --- | .-- --- .-. .-.. -.. in English is HELLO WORLD

請注意，兩者之間的轉換略有不同。 對於英語，我們在“”周圍進行拆分，以單獨獲取每個字符並使用映射。 為了將莫爾斯電碼轉換為英語，我們在“”周圍進行了拆分，因為我假設在將英語單詞轉換為莫爾斯電碼時，給您的摩爾斯電碼字母是您輸出的格式，以空格分隔。 最后，每當我們從英語到摩爾斯電碼並且沒有映射時，我們都填寫“ |” 從摩爾斯電碼轉換為英文時會顯示“”。

祝好運！