Java RegEx: Replace part of source string

Question

If the source string contains the pattern, then replace it with something or remove it. One way to do it is to do something like this

Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(sourceString);
while(m.find()){
  String subStr = m.group().replaceAll('something',""); // remove the pattern sequence
  String strPart1 = sourceString.subString(0,m.start());
  String strPart2 = sourceString.subString(m.start()+1);
  String resultingStr = strPart1+subStr+strPart2;
  p.matcher(...);
}

But I want something like this

Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(sourceString);
    while(m.find()){
      m.group.replaceAll(...);// change the group and it is source string is automatically updated    
}

Is this possible?

Thanks

'something' that wouldn't compile, it's not a character but a string. — Thomas
– Thomas, Commented Oct 14, 2011 at 7:42
Do you mean you want to replace a pattern in your string with something else? Did you try String#replaceAll("pattern","replacement")? — Thomas
– Thomas, Commented Oct 14, 2011 at 7:43

aioobe · Accepted Answer · 2011-10-14 07:50:48Z

// change the group and it is source string is automatically updated

There is no way what so ever to change any string in Java, so what you're asking for is impossible.

To remove or replace a pattern with a string can be achieved with a call like

someString = someString.replaceAll(toReplace, replacement);

To transform the matched substring, as seems to be indicated by your line

m.group().replaceAll("something","");

the best solution is probably to use

A StringBuffer for the result
Matcher.appendReplacement and Matcher.appendTail.

Example:

String regex = "ipsum";
String sourceString = "lorem ipsum dolor sit";

Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(sourceString);
StringBuffer sb = new StringBuffer();

while (m.find()) {
    // For example: transform match to upper case
    String replacement = m.group().toUpperCase();
    m.appendReplacement(sb, replacement);
}

m.appendTail(sb);

sourceString = sb.toString();

System.out.println(sourceString); // "lorem IPSUM dolor sit"

Thomas · Accepted Answer · 2011-10-14 07:45:18Z

2

Assuming you want to replace all occurences of a certain pattern, try this:

String source = "aabbaabbaabbaa";
String result = source.replaceAll("aa", "xx");  //results in xxbbxxbbxxbbxx

Removing the pattern would then be:

String result = source.replaceAll("aa", ""); //results in bbbbbb

answered Oct 14, 2011 at 7:45

Thomas

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2 Comments

aioobe Over a year ago

This is a good approach unless you need to transform the matched substring.

Ali Over a year ago

@aioobe Exactly, I was struggling to explain that. That exactly what I want to do. To transform the matched substring and somehow put it back in the original string.

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