Java replaceall except first and last character in every word

Question

What I want to accomplish is to replace a sentence to underscore, but except the first and last character in a word.

Example:

I am walking

To:

I am w_____g

Is this possible with regex?

When I take the sentence `"I am walking"` and replace everything except the first and last character to a underscore, I get `"I__________g"`. You need to be way more precise, and post an example that makes sense. Also, you need to show what you have tried, as we're willing to help you, but we are not here to fulfill code requests. — jlordo, May 28 '13 at 21:50
You are saying *but except the first and last character in a sentence*, but you gave an example `I am w_____g`. This is not the first and the last character in the sentence it's in the word, explain to us please you need in the word or the sentence? — Azad, May 28 '13 at 21:52

arynaq · Accepted Answer · 2013-05-28T23:13:06.870

This answer should work, in future be a bit more detailed in your questions and do tell us what you have tried, people are more willing to help then ;)

public static void main(String[] args) {
    System.out.println(replaceAll("Hello", '_'));

    String sentence = "Hello Mom What Is For Dinner?";
    StringBuilder sentenceReformed = new StringBuilder();

    for (String word : sentence.split(" ")) {
        sentenceReformed.append(replaceAll(word, '_'));
        sentenceReformed.append(" ");
    }

    System.out.println(sentenceReformed);
}

public static String replaceAll(String word, char replacer) {
    StringBuilder ret = new StringBuilder();
    if (word.length()>2) {
        ret.append(word.charAt(0));
        for (int i = 1; i < word.length() - 1; i++) {
            ret.append(replacer);
        }
        ret.append(word.charAt(word.length() - 1));
        return ret.toString();
    }

    return word;
}

Out:

H__o
H___o M_m W__t Is F_r D_____?

This is working, but is it possible including white spaces? Like: H___o M_m — Cyto, May 28 '13 at 22:43
That is not a word, that is a sentence, you can use the code above for every word in the sentence, see my update. — arynaq, May 28 '13 at 23:04

npr · Answer 2 · 2013-05-29T00:18:40.780

I think you could do this with regular expressions, by looking at where the matches start and end. However, it seems like in this case regular expressions are overkill. It is simpler to allocate a new character array, copy the first and last character of the input to that array, and the fill in the middle with underscores, then allocate a string from that character array, like so:

public class ReplaceMiddle {

public static String replaceMiddle (String s) {
  char[] c = new char[s.length()];

  c[0] = s.charAt(0);

  for (int i = 1; i < s.length() - 1; i++) {
    c[i] = '_';
  }

  c[s.length() - 1] = s.charAt(s.length() - 1);

  return new String(c);

}

public static void main(String[] argv) {
   System.out.println( ReplaceMiddle.replaceMiddle("I want a pumpkin."));
}

}

Output:

I_______________.

Note that this does not handle zero length strings, or the case of s being null.

Java replaceall except first and last character in every word

2 Answers2