Use character wrapper to code a replace a letter in a string with a new letter keeping the original case

Question

Trying to figure out how to use character wrapping to mutate a string based on user input. If string is \'Bob loves to build building\' and user chooses to replace all letter B/

Answer 1

I think there is a String class built-in replace function.

String text = "Bob loves to build building";
text = text.replace("B","T").replace("b","t");

something like this ?

Answer 2

Your question is unclear (how 'b' becomes 'm' in Bob -> Tom?). However, to run case insensitive replace you should do something like this:

String text ="Bob loves to build building";
String b = "b";

Pattern p = Pattern.compile(b, Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(text);

String outText = m.replaceAll("T");

Answer 3

A simple start is to know about String.replace(char, char) in Java.

// This addresses the example you gave in your question.
str.replace('B', 'T').replace('b', 't');

Then, you should take the user input into toReplace and replaceWith characters, figure out the uppercase/lowercase counter parts using the ASCII code and generate the arguments for the above replace method call.

public class Main
{
    public static void main(String[] arg) throws JSONException
    {
        String str = "Bob loves to build building";
        Scanner scanner = new Scanner(System.in);
        char toReplace = scanner.nextLine().trim().charAt(0);
        char replaceWith = scanner.nextLine().trim().charAt(0);

        System.out.println(str.replace(getUpper(toReplace), getUpper(replaceWith)).replace(getLower(toReplace),
            getLower(replaceWith)));
    }

    private static char getUpper(char ch)
    {
        return (char) ((ch >= 'A' && ch <= 'Z') ? ch : ch - ('a' - 'A'));
    }

    private static char getLower(char ch)
    {
        return (char) ((ch >= 'A' && ch <= 'Z') ? ch + ('a' - 'A') : ch);
    }
}