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


i working on morse code english java code (below) in | in morse stands blank space between letters , numbers, , blank space in morse stands in between 2 letters or digits. ex., "to be" = "- --- | -... ." in morse.

// 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 translate 'morse code' english, or 'english' morse code? (enter 'morse code' or 'english'.)");     string unit1 = input.nextline();     system.out.println("enter string of " + unit1 + " characters (for english, numbers , 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 single quotes."); }      public static void tomorsecode(string english) {     // declare variables, arrays, , strings.     int = 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();      // loops , if statements result.     (i = 0; < 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];     // loops , if statements result.     (i = 0; < 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 " + morsebuilder + "."); }  public static void toenglish(string morse) {     // declare variables, arrays, , strings.     int = 0;     int l = morse.length();     int i2 = / 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();      // loops , if statements result.     (i = 0; < l; i++)     {         i2 = / 2;         if (morse.charat(i) == '|')         {             englishbuilder.append(' ');         }         else             englishbuilder.append(morsecode[i2]);     }      morsecode[i] = loweralphabet[i];     // loops , if statements result.     (i = 0; < l; i++)     {         i2 = / 2;         if (morse.charat(i) == '|')         {             englishbuilder.append(' ');         }         else             englishbuilder.append(morsecode[i2]);     }      // display results.     system.out.println("the corresponding english " + englishbuilder + ".");     } }

i getting error:

would translate 'morse code' english, or 'english' morse code? (enter 'morse code' or 'english'.) english enter string of english characters (for english, numbers , letters, only):  exception in thread "main" java.lang.stringindexoutofboundsexception: string index out of range: -1     @ java.lang.abstractstringbuilder.charat(abstractstringbuilder.java:237)     @ java.lang.stringbuilder.charat(stringbuilder.java:76)     @ project1_szhu1249322.tomorsecode(project1_szhu1249322.java:42)     @ project1_szhu1249322.main(project1_szhu1249322.java:16)

i not understand why giving me error message.

also (question 2), i2 value should use? / 2 works (when first character not blank space. help???

you failing on morsebuilder.charat(i - 1) when i==0


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