how to replace string in java?

Question

I have a String str = "a_bcde_fghij_k".

and I want to change it to "aBcdeFghijK"

If have a _ character, the next character will be change to uppercase and remove _ character.

How can I do this?

possible duplicate of How to replace special characters in a string? — Adam Arold
– Adam Arold, Commented Jul 16, 2013 at 8:35
@AdamArold: I don't see how it's a duplicate of that at all. What part of that deals with "upper-case the next letter"? — Jon Skeet
– Jon Skeet, Commented Jul 16, 2013 at 8:37
What is supposed to happen when there are two underscores (like "__a")? — f1sh
– f1sh, Commented Jul 16, 2013 at 8:37

Jon Skeet · Accepted Answer · 2013-07-16 14:02:41Z

10

I suspect you'll need to just go through this character by character, building up the string as you go. For example:

public static String underscoreToCapital(String text) {
    // This will be a bit bigger than necessary, but that shouldn't matter.
    StringBuilder builder = new StringBuilder(text.length());
    boolean capitalizeNext = false;
    for (int i = 0; i < text.length(); i++) {
        char c = text.charAt(i);
        if (c == '_') {
            capitalizeNext = true;
        } else {
            builder.append(capitalizeNext ? Character.toUpperCase(c) : c);
            capitalizeNext = false;
        }
    }
    return builder.toString();
}

edited Jul 16, 2013 at 14:02

answered Jul 16, 2013 at 8:40

Jon Skeet

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8 Comments

m0skit0 Over a year ago

I think regexes give much simpler code, but probably a slower one.

m0skit0 Over a year ago

Oh btw it's text.length() ;)

Jon Skeet Over a year ago

@m0skit0: Fixed, thanks. But I still prefer this over the regex version :)

m0skit0 Over a year ago

@JonSkeet Ok I understand :) But I've learned a lesson: never waste my time again writing answers when you answer xD Have a nice day! :)

m0skit0 Over a year ago

@JonSkeet +10 upvotes and accepted... but this is not working. Did anyone try this? For input a_acde_fghij_k it returns AaCDEfGHIJk, which as I understood the question, is wrong. This capitalizeNext ? c : Character.toUpperCase(c) looks like swapped up.

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Joachim Sauer · Accepted Answer · 2013-07-16 08:40:55Z

4

Regular expressions alone can't do that (there is no "touppercase" operator, so to speak).

But Guava has a nice little utility called CaseFormat that can help you:

String result = CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, str)

This works, even 'though your input is not strictly in UPPER_UNDERSCORE format, but CaseFormat is lenient this way (if you want the first character to be capitalized as well use UPPER_CAMEL instead).

Alternatively, if you absolutely want to use regular expressions, you can use Matcher.appendReplacement (it has a nice example in the JavaDoc):

public static final Pattern UNDERSCORE_FOLLOWED_BY_ANYTHING = Pattern
        .compile("_(.)");

public static String toUpperAfterUnderscore(String input) {
    Matcher m = UNDERSCORE_FOLLOWED_BY_ANYTHING.matcher(input);
    StringBuffer sb = new StringBuffer();
    while (m.find()) {
        m.appendReplacement(sb, m.group(1).toUpperCase());
    }
    m.appendTail(sb);
    return sb.toString();
}

answered Jul 16, 2013 at 8:40

Joachim Sauer

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2 Comments

m0skit0 Over a year ago

Nice answer, useful info but hmmm external libraries... +1 anyway

Joachim Sauer Over a year ago

@m0skit0: Guava contains so many useful little utilities, that it really ought to be a dependency of every non-trivial project (and quite a few trivial ones).

Mark M · Accepted Answer · 2013-07-16 08:49:51Z

2

You can also try splitting.

String str = "a_bcde_fghij_k"
String result[] = str.split("_");
String newstr = result[0];
for (int i=1;i<result.length;i++) {
     char first = Character.toUpperCase(result[i].charAt(0));
     newstr = newstr + first + result[i].substring(1);
}
System.out.println(newstr);

split() takes regex, if you feel that is important.

answered Jul 16, 2013 at 8:49

Mark M

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1 Comment

Joachim Sauer Over a year ago

This also uses String for concatenation, it should really use StringBuilder (or at least StringBuffer), they are made to be manipulated.

ridoy · Accepted Answer · 2013-07-16 11:59:59Z

1

A slightly different approach from me but works good..

  String str = "a_bcde_fghij_k";
  int count=0;
  String[] splitString = (str.split("_"));

  for (String string : splitString)
  {
    count++;        
    if(count>1)
    {
        char c= string.charAt(0);
        System.out.print(string.replace(c, Character.toUpperCase(c)));
    }
    else
        System.out.print(string);
  }

Isn't it?

edited Jul 16, 2013 at 11:59

answered Jul 16, 2013 at 11:49

ridoy

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Comments

m0skit0 · Accepted Answer · 2013-07-16 08:57:39Z

0

There's no straight away way to do it with regexes, but I think using regexes can greatly simplify the task:

public static String underscoreToCapital(final String input) {
    String ret = input;
    final Matcher m = Pattern.compile("_([a-z])").matcher(input);
    while (m.find()) {
        final String found = m.group();
        final String toUppercase = m.group(1);
        ret = ret.replaceAll(found, toUppercase.toUpperCase());
    }
    return ret;
}

edited Jul 16, 2013 at 8:57

answered Jul 16, 2013 at 8:51

m0skit0

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4 Comments

Jon Skeet Over a year ago

I don't think that's simpler, personally. (I retract my suggestion that it doesn't work, but I still don't think it's as clear as just iterating.)

m0skit0 Over a year ago

Input: a_acde_fghij_k Ouput: a_Acde_Fghij_K Is this what you mean? Also edited it to match the question, I was keeping the underscore...

m0skit0 Over a year ago

@JonSkeet answer edit made your comment right :) Edited it again so now it does work correctly.

m0skit0 Over a year ago

@JonSkeet I do think it's more readable and maintainable than iterating over all the characters (probably because I'm used to working with regexes). Also shorter code means lesser bugs ;) And your comment about it not working was definitely right, thanks for correcting.

Enrichman · Accepted Answer · 2013-07-16 08:57:40Z

0

You have to do probably some check on the execution of this method but this could be another idea:

public String replaceAndUpper(String word) {
    int charToRemove = word.indexOf("_");
    while (charToRemove != -1) {
        String part1 = word.substring(0, charToRemove);
        String part2 = word.substring(charToRemove + 1);
        char upperChar = Character.toUpperCase(part2.charAt(0));
        word = part1 + String.valueOf(upperChar) + part2.substring(1);
        charToRemove = word.indexOf("_");
    }
    return word;
}

answered Jul 16, 2013 at 8:57

Enrichman

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7 Comments

giorashc Over a year ago

You should use a StringBuilder/Buffer (for building the result) which are used for these kind of concatenations (provides better performance)

Enrichman Over a year ago

Yep, that could be an improvement. Btw, the '+' should be internally converted to use a StringBuilder if I'm not wrong.

m0skit0 Over a year ago

Also too much calls to substring. Using String#charAt() is way better.

m0skit0 Over a year ago

@Enrichman You're wrong.

Enrichman Over a year ago

How do you split then? With charAt I can get the Character to remove/capitalize, but thenk I have to split and rebuild the String.

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