java - java项目中文本加解密的编写方法

Question

在让我的代码正常运行时遇到问题，第一部分可以正常工作，它会加密输入的代码并打印结果，但是当函数进入方法转换字母表时，我会受到欢迎

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: begin 0, end -1, length 0.

当我在这里苦苦挣扎时，有人可以向我解释我的项目哪里出了问题。

代码如下。

import java.util.*;

public class Main {

    public static void  main(String[] args) {
        Scanner sc = new Scanner( System.in );
        String encryptedText;
        int encryptedNumber;
        int length;

        System.out.println("Please input text to encrypt");
        encryptedText = sc.nextLine();
        System.out.println("Enter a number for encryption amount");
        encryptedNumber = sc.nextInt();
        System.out.println("Enter a length for your segment");
        length = sc.nextInt();
        System.out.println("Thank you for your input");

        String compressedvalue = encryptString(encryptedText,encryptedNumber,length);
        System.out.println(" Your encrypted value is:" + compressedvalue);

        String decryptedText = ungroupify(compressedvalue);
        System.out.println("The decryption algorithm produced: "  + decryptedString(decryptedText,encryptedNumber));
        System.out.println("Thank you");

        normalizeText(""  );
    }


    // Part 1 Normalized Method to convert all letter to uppercase and removing all special characters and placing it into String codey.
    public static String normalizeText (String codey){

        System.out.println(codey.replaceAll(" ","").replaceAll("[^a-zA-Z ]", "").toUpperCase());

        System.out.println(codey);
        obify("");
        return normalizeText(codey);

    }

    public static String obify(String input){
        String obifiledInput="";
        char[] vowels={'A','E','I','O','U','Y'};
        for (int i=0;i<input.length();i++){
            boolean flagVowelNotHave=true;
            for(int j=0;j<vowels.length;j++){
                if (input.charAt(i)==vowels[j]){
                    obifiledInput+=("OB"+input.charAt(i));
                    flagVowelNotHave=false;
                }
            }
            if(flagVowelNotHave)obifiledInput+=input.charAt(i);
        }
        ceasarify("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 26);

        return obifiledInput;

    }

    public static String ceasarify(String a, int n){
        String letterIndex = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" ;
        String returnString = "";

        for (int cnt = 0; cnt < a.length(); cnt++) {
            char oLetter = a.charAt(cnt);
            int oIndex = letterIndex.indexOf(oLetter);
            int nIndex = oIndex + n;
            if (nIndex >= 0) {
                if (nIndex > 25) {
                    while (nIndex > 25) { nIndex -= 26; }
                }
            }
            else {
                while (nIndex < 0) { nIndex += 26; }
            }
            returnString = returnString + letterIndex.charAt(nIndex);
        }
        groupify( "", 26 );
        return returnString;

    }

    public static String groupify( String p, int f){
        int newy = p.length();
        String segmented = "";
        int bigLength = newy % f;

        for (int chop = 0; chop < newy; chop += f) {
            if (chop + f > newy) {
                segmented = segmented + p.substring(chop, newy);
                for (int x = 0; x < bigLength; x++) {
                    segmented = segmented + "x";
                }
            }
            else { segmented = segmented + p.substring(chop, chop + f) + " "; }
        }


        if (bigLength == 0) { segmented = segmented.substring(0,segmented.length() - 1); }

        shiftAlphabet(0);
        return segmented;
    }

    public static String shiftAlphabet(int shift) {
        int start = 0;
        if (shift < 0) {
            start = (int) 'Z' + shift + 1;
        } else {
            start = 'A' + shift;
        }
        String result = "";
        char currChar = (char) start;
        for(; currChar <= 'Z'; ++currChar) {
            result = result + currChar;
        }
        if(result.length() < 26) {
            for(currChar = 'A'; result.length() < 26; ++currChar) {
                result = result + currChar;
            }
        }

        encryptString("",26,25);
        return result;
    }

    public static String encryptString(String code, int shifty, int big) {

        String ntext = normalizeText(code);
        String ctext = ceasarify(ntext,shifty);
        String gtext = groupify(ctext,2 );

        return gtext;
    }

    private static String decryptedString (String decryptedText, int encryptedNumber) {
        String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        encryptedNumber = encryptedNumber * -1; //Reverse the value.
        String bigText = "";

        for (int i = 0; i < decryptedText.length(); i++) {
            int oldText = alphabet.indexOf(decryptedText.charAt(i));
            int newText = oldText + encryptedNumber;

            // Wrap if longer/shorter than alphabet.
            if (newText < 0) { while(newText < 0) { newText += 26; } }
            else if (newText > 25) { while(newText > 25) { newText -= 26; } }

            bigText = bigText + alphabet.charAt(newText);
        }
        return bigText;
    }

    private static String ungroupify (String compressedvalue) {
        compressedvalue = compressedvalue.replace("x", ""); //Remove space-filling x's
        compressedvalue = compressedvalue.replace(" ", ""); //Remove spaces.
        return compressedvalue;
    }

}

标签： javamethodsparametersreturndo-while

Answer 1

您传入的第一个参数groupify是“”。

当groupify方法被调用时，for循环被跳过并且segmented.substring(0, 0-1);函数抛出IndexOutofBound异常。