Java - Regular Expression

Group

Regular Expression - Group (Capture|Substitution)

Capturing groups are numbered by counting their opening parentheses from left to right.

Example: expression ((A)(B(C))) are four such groups:

• 1: ((A)(B(C)))
• 2: (A)
• 3: (B(C))
• 4: (C)

Pattern pattern = Pattern.compile("((A)(B(C)))");
Matcher matcher = pattern.matcher("myInputString");
Assert.assertEquals("There is 4 groups in this pattern", 4, matcher.groupCount());

Iterate

Example on how to iterate over the pattern matches.

String sourceText = "ABC";
Pattern pattern = Pattern.compile("((A)(B(C)))");
Matcher matcher = pattern.matcher(sourceText);

// Number of find
Integer seqCounter = 1;
// Matcher try to find the first sequence match
while (matcher.find()) {

	seqCounter++;
	
	System.out.println();
	System.out.println("Sequence " + seqCounter);

	for (int i = 0; i <= matcher.groupCount(); i++) {

		System.out.printf(i + " : " + matcher.group(i));
		if (i == 0) {
			System.out.printf(" (the index 0 contains the whole string that matches)\n");
		} else {
			System.out.printf("\n");
		}
	}
	
}

Sequence 2
0 : ABC (the index 0 contains the whole string that matches)
1 : ABC
2 : A
3 : BC
4 : C

Parsing bash parameters

String text = "$1 love $2";
Pattern pattern = Pattern.compile("(\\$([0-9]))");
// to catch $1 and $2
Matcher matcher = pattern.matcher(text);
System.out.println("There is "+matcher.groupCount()+" group in the pattern");
int matchCount = 0;
while (matcher.find()) {
	matchCount++;
	System.out.println("Value for the "+matchCount+" match");
	for (int i=0;i<=matcher.groupCount();i++) {
		System.out.println(" - Group "+i+": "+ matcher.group(i));
		if (i==0){
			System.out.println("  The group 0 represents always the whole expression");
		}
	}
}

Output:

There is 2 group in the pattern
Value for the 1 match
 - Group 0: $1
  The group 0 represents always the whole expression
 - Group 1: $1
 - Group 2: 1
Value for the 2 match
 - Group 0: $2
  The group 0 represents always the whole expression
 - Group 1: $2
 - Group 2: 2

Search and replace

• JEdit - Search and Replace

Flag

Flags need to be in the pattern expression.

Example with an insensitive match for the letter xxx:

Pattern pattern = Pattern.compile("(?i:xxx)");

You can see them in the doc

(?idmsux-idmsux:X) 

where X is a non-capturing group with the given flags i d m s u x on, with - off.