从 txt 文件中读取字符串并将其存储到 java 中的 char 数组中

Question

I am new to java. I am trying to read a text file and store the variables it into an array char by char then apply Caesar Cipher encryption to it. However I am getting ejava.lang.StringIndexOutOfBoundsException: String index out of range: 4 on the line that says if (str.charAt(i) == str.charAt(j)) If someone could help,that would be great!

PROBLEM SOLVED*

public void passwordCaesaCipher() throws Exception {
        String str;
        int size = 0;
        char[] string1 = {};
        File f = new File("password.txt");
        BufferedReader br = new BufferedReader(new FileReader(f));
        String lowercase = "abcdefghijklmnopqrstuvwxyz";

        while ((str = br.readLine()) != null) {
            System.out.println(str);
            string1 = str.toCharArray();
            size = str.length();
            System.out.println(size);
            System.out.println(string1);
            for (int i = 0; i < size; i++) {
                for (int j = 0; j < 26; j++) {
                    if (str.charAt(i) == lowercase.charAt(j)) {
                        System.out.print(str.charAt((j) % 26));
                    }
                    else
                    {
                        
                    }

                }
            }
            System.out.println();

        }

    }

My text file has "abc" and I want it to be "bcd". However with my implementation I am getting abc.

Answer 1

You might want to check the length for the 2nd for loop that is 26. When the string that you read from the file is less than 26 of length, it will always result to index out of range.

Answer 2

Editing the second loop helped me to achieve the correct answer. I forgot to add +1 to System.out.print(lowercase.charAt((j) % 26)); . Because of that it was just printing itself. Correct solution is: System.out.print(lowercase.charAt((j+1) % 26));