Playfair密码，保持良好状态

Question

我有下面的代码，但不断收到错误，但文件生成OK，我相当新的所有这一切。

就像我说的文件建立好，它接受输入1 & 2并给出了选项，但一直给我一个例外。它会询问关键字和明文，但是在解密或加密下面的错误时出现。

对不起我在queston第一次尝试..希望这是一个好一点......

异常线程“main” java.lang.StringIndexOutOfBoundsException：3：字符串索引超出范围 java.lang.String.charAt（String.java:695）at playfair.format（playfair.java:123）at playfair.Divid2Pairs（playfair.java:135）at playfair.Encript（playfair.java:187 ）at playfair.main（playfair.java:332）

import java.util.Scanner; 

public class playfair { 

    private String KeyWord=new String(); 
    private String Key=new String(); 
    private char matrix_arr[][]= new char[5][5]; 

    public void setKey(String k){ 

     // This function will take the input key from the user 
     // Then it'll remove duplication of letters from the key 
     // Will add it to the private KeyWord for matrix generation 

     String K_adjust=new String(); 
     boolean flag = false; 

     K_adjust = K_adjust + k.charAt(0); 

     for(int i=1; i<k.length();i++){ 

      for(int j=0;j<K_adjust.length(); j++){ 

       if(k.charAt(i)==K_adjust.charAt(j)) 
       { 
        flag = true; 
       } 
      } 

      if(flag == false){ 
       K_adjust = K_adjust + k.charAt(i); 
      } 
      flag = false; 
     } 

     KeyWord=K_adjust; 
    } 

    public void KeyGen() 
    { 
    // This function adjust the alphabetical letters adding the 
    // KeyWord on the beginning of them & then it calls the matrix function 

    boolean flag=true; 
    char current; 

    Key=KeyWord; 

    for (int i=0 ; i<26 ; i++){ 

     current=(char)(i+97); 

     if(current=='j') 
     continue; 

     for(int j=0 ; j< KeyWord.length() ; j++){ 

      if (current == KeyWord.charAt(j)){ 

       flag=false; 
       break; 
      } 
     } 

     if(flag) 
     Key=Key+current; 

     flag=true; 
    } 

    System.out.println(Key); 
    matrix(); 

    } 

    private void matrix() 
    { 
    int counter=0; 

    for (int i=0 ; i<5 ;i++){ 

     for (int j=0 ; j<5 ; j++){ 

      matrix_arr[i][j]=Key.charAt(counter); 
      System.out.printf("%s ",matrix_arr[i][j]); 

      counter++; 
     } 

     System.out.println("\n"); 
    } 
    } 

    private String format(String old_text) 
    { 
    // This function is to adjust the Text to encrypt 
    // It changes all the 'j' letters to 'i' & add 'x' character 
    // between repeatable pairs. 

    int i = 0; 
    int j = 0; 
    int len = 0; 
    String text = new String(); 
    len = old_text.length(); 

    //System.out.println(old_text); 
    /*** Change all j's into i's *****/ 
    for (int tmp = 0; tmp < len; tmp++) 
    { 
     if (old_text.charAt(tmp) == 'j') 
     { 
      text = text + 'i'; 
     } 
     else 
      text = text+old_text.charAt(tmp); 
    } 
    /**********************************/ 
    len = text.length(); 
    /*** Assign 'x' to letters that repeat in a diagram ***/ 
    for (i = 0; i < len; i = i + 2){ //run for half of string length 

     if (text.charAt(i+1) == text.charAt(i)){ //if char = previous char 

      text = text.substring(0, i+1) + 'x' + text.substring(i+1); 
     }else{ //not a repeat character, move along 
     } 
    } 
    return text; 
    } 

    private String [] Divid2Pairs (String new_string) 
    { 
     String Original = format(new_string); 

     int size= Original.length(); 

     if(size%2!=0){ 
      size++; 
      Original = Original+'x'; 
     } 

     String x[]= new String[size/2]; 

     int counter=0; 

     for (int i=0 ; i<size/2 ;i++){ 
      x[i]=Original.substring(counter, counter+2); 
      System.out.println(x[i]); 
      counter=counter+2; 
     } 

     return x; 
    } 

    public int[] GetDiminsions(char letter){ 

     int []key=new int[2]; 

     if (letter == 'j') 
     letter='i'; 

     for (int i=0 ; i<5 ;i++) 
     { 
      for (int j=0 ; j<5 ; j++){ 

       if(matrix_arr[i][j] == letter){ 

        key[0]=i; 
        key[1]=j; 
        break; 
       } 
      } 

     } 

     return key; 
    } 

    public String Encript(String Source) 
    { 
     System.out.println("Encription Start"); 

     String src_arr[]=Divid2Pairs(Source); 

     String Code=new String(); 

     char one; 
     char two; 

     int part1[]=new int[2]; 
     int part2[]=new int[2]; 

     //start on pair by pair 
     for (int i=0 ; i< src_arr.length ;i++){ 
      one = src_arr[i].charAt(0);//get first char 
      two = src_arr[i].charAt(1);//get second char 

      part1 = GetDiminsions(one);//get position of the first char 
      part2 = GetDiminsions(two);//get position of the second char 

      //check for special cases 
      if(part1[0]==part2[0]){//same row 

       if (part1[1]<4) 
        part1[1]++; 
       else 
        part1[1]=0; 

       if(part2[1]<4) 
        part2[1]++; 
       else 
        part2[1]=0; 

      } 

      else if (part1[1]==part2[1]) //same column 
      { 
      if (part1[0]<4) 
      part1[0]++; 
      else 
      part1[0]=0; 

      if(part2[0]<4) 
      part2[0]++; 
      else 
      part2[0]=0; 
      } 
      else 
      { 
      int temp=part1[1]; 
      part1[1]=part2[1]; 
      part2[1]=temp; 
      } 

      Code= Code + matrix_arr[part1[0]][part1[1]] + matrix_arr[part2[0]][part2[1]]; 
      } 
     System.out.println(Code); 
     return Code; 
    } 

    public String Decript (String Code){ 
     System.out.println("Decription Start"); 

     String Original=new String(); 

     String src_arr[]=Divid2Pairs(Code); 

     char one; 
     char two; 

     int part1[]=new int[2]; 
     int part2[]=new int[2]; 


     //start on pair by pair 
     for (int i=0 ; i< src_arr.length ;i++){ 
      one = src_arr[i].charAt(0);//get first char 
      two = src_arr[i].charAt(1);//get second char 

      part1 = GetDiminsions(one);//get position of the first char 
      part2 = GetDiminsions(two);//get position of the second char 

      //check for special cases 
      if(part1[0]==part2[0]){//same row 

       if (part1[1]>0) 
        part1[1]--; 
       else 
        part1[1]=4; 

       if(part2[1]>0) 
        part2[1]--; 
       else 
        part2[1]=4; 
      } 

      else if (part1[1]==part2[1]) //same column 
      { 
      if (part1[0]>0) 
      part1[0]--; 
      else 
      part1[0]=4; 

      if(part2[0]>0) 
      part2[0]--; 
      else 
      part2[0]=4; 
      } 
      else 
      { 
      int temp=part1[1]; 
      part1[1]=part2[1]; 
      part2[1]=temp; 
      } 


      Original =Original + matrix_arr[part1[0]][part1[1]] + matrix_arr[part2[0]][part2[1]]; 
      } 

     System.out.println(Original); 
     return Original; 
    } 
    /** 
    * @param args 
    */ 
    public static void main(String[] args) { 
     // TODO Auto-generated method stub 

     playfair x=new playfair(); 

     Scanner sc = new Scanner(System.in); 

     System.out.println("Enter a lower case keyword:"); 
     String keyword = sc.next(); 
     x.setKey(keyword); 
     x.KeyGen(); 

     System.out.println("To Encrypt enter 1 \nTo Decript enter 2\nTesting both enter anything else:"); 
     int choosen_value = sc.nextInt(); 

     if(choosen_value==1) 
     { 
      System.out.println("Enter a lower case word to encrypt:"); 
      String key_input = sc.next(); 
      String Encripted= x.Encript(key_input); 
     }else if(choosen_value==2){ 
      System.out.println("Enter a lower case word to decrypt:"); 
      String decripted = sc.next(); 

      x.Decript(decripted); 
     }else{ 
      System.out.println("Enter a lower case word to encrypt & decrypt:"); 
      String key_input = sc.next(); 

      String Encripted= x.Encript(key_input); 
      x.Decript(Encripted); 
     } 
    } 
} 

提前

Answer 1

在format方法中，在以下环

for (i = 0; i < len; i = i + 2) 

text.charAt(i+1)是造成问题的原因的行。

您需要遍历直到len-1而不是len。

这是因为当i正是1比len，它还是会在charAt()方法执行for循环，但i+1将尝试指数len(since i+1 is now equal to len)，它抛出StringIndexOutOfBoundsException作为最大可访问的，以获取char本字符串中的索引是str.length()-1。

Answer 2

(i = 0; i < len; i = i + 2)再次感谢引起异常

，你可能需要做i<len-1这里。