How do I remove a character from a String?

public static String removeChar(String s, char c) {
  StringBuffer r = new StringBuffer( s.length() );
  r.setLength( s.length() );
  int current = 0;
  for (int i = 0; i < s.length(); i ++) {
     char cur = s.charAt(i);
     if (cur != c) r.setCharAt( current++, cur );
  }
  return r.toString();
}

I've found the above code here.

Two Questions:

1. why 开发者_JS百科do we need to do setLength()? without which I am getting java.lang.StringIndexOutOfBoundsException: String index out of range: 0

2. 'ttr' and three junk chars are coming when I run this program with parameters - "teeter" and "e". How to remove the unused whitespaces in the buffer?

Why not just use replaceAll? java.lang.String.replaceAll

I'll answer your questions:

1 - why do we need to do setLength()? without which I am getting java.lang.StringIndexOutOfBoundsException: String index out of range: 0

Initially your string buffer has no characters. You need to call setLength in order to populate your empty string buffer with characters. Null characters, '\0', (or junk characters as you call them) are added to the string buffer so that it reaches the specified length. If you don't, you get a StringIndexOutOfBoundsException because there are no characters in your string buffer. See Javadocs on StringBuffer#setLength.

So at the end of your method your string buffer has: [t][t][r][\0][\0][\0]

2 - 'ttr' and three junk chars are coming when I run this program with parameters - "teeter" and "e". How to remove the unused whitespaces in the buffer?

You can remove the null characters by calling: r.toString().trim() or r.substring(0,current)

It seems like you would just want to use the String.replaceAll(OLD, NEW);

Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array.

API - http://download.oracle.com/javase/6/docs/api/java/lang/StringBuffer.html

Secondly you can just call trim on the string if you want to remove whitespace from the beginning and the end.

But, the other comments suggesting you should use replace/replaceAll are the most pertinent ones. Why rewrite an inbuilt method.

http://download.oracle.com/javase/6/docs/api/java/lang/String.html#replace(char, char)

Ignoring the fact you can use String.replaceAll()...

You should use the append method:

  public static String removeChar(final String s, final char c) {
    final StringBuffer r = new StringBuffer(s.length());
    for (int i = 0; i < s.length(); i++) {
      final char cur = s.charAt(i);
      if (cur != c) {
        r.append(cur);
      }
    }
    return r.toString();
  }

Now you won't get the StringIndexOutOfBoundsException.

BTW, in a single threaded environment you should really use StringBuilder.

There is a simpler solution:

public static String removeChar(String s, char c) {
    return s.replaceAll(Pattern.quote(new StringBuilder().append(c).toString()), "");
}

You can use:

public static String removeChar(String s, char c) {
    StringBuilder r = new StringBuilder();

    for (int i = 0; i < s.length(); i++) {
        char cur = s.charAt(i);
        if (cur != c) {
            r.append(cur);
        }
    }

    return r.toString();
}