如何在不使用 replace 方法的情况下替换 Java 中的子字符串？

Question

What I need to do is replace the letter the user wants to replace in a string with X. Here's an example:

replaceLetterWithX("asdfgsdfghfghj","s")

aXdfgXdfghfghj

But I can't use the replace method. I also need to use the substring, length, and equals methods. I'm a bit confused about where to start. Here's what my code looks like now:

public static String replaceLetterWithX(String str, String c)
    {
        //This method will return 'str' with all instances of letter 'c' replaced
        //by 'X'

        String result="";
        
        int count = 0;

        //Code here

        return result;
    }

Answer 1

This can be done with a simple for loop using the charAt method. By looping through the strings and comparing each character with the character to be replaced, we can construct the replaced string from scratch. Keep in mind that this is case-sensitive, I suggest you do some research into the Java documentation to learn more about how to do that.

public static String replaceLetterWithX(String str, String c)
    {
        //This method will return 'str' with all instances of letter 'c' replaced
        //by 'X'

        String result="";

        //Code here
        //looping through each character in the string 
        for (int i = 0; i < str.length(); i++)
        {
            //converting the character at i to string and comparing it with the given letter
            if (Character.toString(str.charAt(i)).equals(c))
            {
                result += "X";
            }
            //if it isn't add the original letter in the string
            else
            {
                result += str.charAt(i);
            }
        }
        return result;
    }