在Java中，如何用字符串替换任意字符？

Question

I'm trying to create a method that replaces an individual character in a string with another string so far, these are my parameters.

public static String replaceAt(String str, int position, String replacement)

It's supposed to look something like this when it runs correctly:

method         input                          output

replaceAt     "Hello, World", 5, " comma"     Hello comma World

This is what I have so far.

{
   String result = "";

  char character = str.charAt(position);

  str = str.replace(character, replacement);

  result = str;

  return result;
 }

but I'm pretty sure I'm messing up the syntax somehow, any pointers on how to proceed?

Answer 1

If you can use StringBuilder , then you could instantiate one with your input str and then call StringBuilder#replace(int, int, String) like

public static String replaceAt(String str, int position, String replacement) {
    return new StringBuilder(str).replace(position, position + 1, 
            replacement).toString();
}

If you can't use that, then you might use String#substring(int, int) and concatenate your output like

return str.substring(0, position) + replacement + str.substring(position + 1);

Note that internally uses StringBuilder to perform the concatenation (at least in recent Java releases), so it is equivalent to

return new StringBuilder(str.substring(0, position)).append(replacement)
        .append(str.substring(position + 1)).toString();

(in very old releases StringBuffer was used).

Answer 2

The biggest problem with using replace , or other solutions that search for regexes, is that we don't know whether the character at that position is the only one in the string. Suppose the input string is "Hello, world, good morning" . Then your replaceAt would return "Hello comma world comma good morning" . Maybe that's what you really want (it isn't clear), but a method that pretends to be one that "replaces" the character "at" the given "position" with a string, shouldn't do more than that. (If that's really what you want, I recommend changing the name and the parameters.)

Assuming you want to replace the character at that position, and only the character at that position, I'd recommend using substring instead:

public static String replaceAt(String str, int position, String replacement) {
    return str.substring(0, position) + replacement + str.substring(position + 1);
}

Edit: If you want to handle the case where position == the string length, so that there is no character at that position:

public static String replaceAt(String str, int position, String replacement) {
    return str.substring(0, position) + replacement + (position == str.length() ? "" : str.substring(position + 1));
}

(If position > the string length, the first substring won't work. Depending on the use case, you can let it throw an exception if this case isn't supposed to happen. Or you could do this:)

public static String replaceAt(String str, int position, String replacement) {
    return str.substring(0, Math.min(position, str.length())) + replacement + (position >= str.length() ? "" : str.substring(position + 1));
}