如何在字符串中的每个字符之前插入一个字符，但不在 Java 中的“空格”之前插入一个字符？

Question

This is what I got. It works for now, but if I type, for example, "I like bananas", I get 'pIp ppipkpep pbpapnpapnpaps', while I'm aiming to get 'pI pLpipkpe pbpapnpapnpaps.

Every solution I tried came down to using an 'if statement', trying to check if the character at said position in the original 'encText'is equal to ' ', and if so, making it equal to ' ' as well in the newText array before checking if the position required an 'p' or the char from the original array.. However, everytime I tried that, I'd get an array out of bounds exception.

        static void pEncrypt() {
        System.out.println("Adding P");
        Scanner in = new Scanner(System.in);
        String encText = in.nextLine();
        int k = encText.length();

        char[] charsEncText = encText.toCharArray();
        char[] newText = new char[2*k];

        int j = 1;

        for (int i = 0; i < (k*2); i++) {
             if (i%2 == 0) {
                newText[i] = 'p';
            } else {
                newText[i] = charsEncText[i-j];
                j++;

            }
        }
        System.out.println(newText);
    }

Answer 1

A simpler solution is to use replaceAll with a positive lookahead .

String str = "I like bananas";
String res = str.replaceAll("(?=[^ ])", "p");
System.out.println(res); // "pI plpipkpe pbpapnpapnpaps"

Demo

Answer 2

Assuming one does not need a char[] , I would just concatenate to a String . Something like:

    public static String pEncrypt(String org)
    {
        String ret = "";
        
        for (int i = 0; i < org.length(); ++i) {
            char ch = org.charAt(i);
            if (ch != ' ') {
                ret += "p" + ch;
            }
            else {
                ret += ' ';
            }
        }
        
        return ret;
    }

Also, to make things a bit easier, it is generally a good idea to separate the I/O (ie, the Scanner and the println ) from the processing. That way, one can write test cases rather than attempting to keep inputting the information.

Sample Output:

helloworld ==> phpeplplpopwpoprplpd
I like bananas ==> pI plpipkpe pbpapnpapnpaps

Answer 3

You can try this way.

        static void pEncrypt() {
        System.out.println("Adding P");
        Scanner in = new Scanner(System.in);
        String encText = in.nextLine();
        int k = encText.length();

        char[] charsEncText = encText.toCharArray();
        char[] newText = new char[2*k];

        int j=0;
    

        for(int i=0;i<k;i++)
        {
            if(charsEncText[i]==' ')
            {
                newText[j]=charsEncText[i];
                j++;
            }
            else{
                newText[j]='p';
                newText[j+1]=charsEncText[i];
                j=j+2;
            }
        }
        System.out.println(newText);
    }