user2533660 user2533660 - 11 days ago 6
Java Question

If statement that is supposed to filter out newline not filtering new lines.

I'm writing a Regex pattern that filters through HTML tags and prints only the contents of valid tags for practice. While the pattern itself appears to be matching tags correctly, I am running into an issue when printing them.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class HTMLPattern{
public static void main(String[] args){

Scanner in = new Scanner(System.in);
int testCases = Integer.parseInt(in.nextLine());

while(testCases>0){
String line = in.nextLine();
String tagPattern = "<([^>]+)>([^<]*?)</\\1>";
Pattern p = Pattern.compile(tagPattern, Pattern.MULTILINE);
Matcher m = p.matcher(line);
if(m.find()){
//checks if the output equals a newline
if(m.group(2).matches("[\\n\\r]+")){
System.out.println("None");
}else{
System.out.println(m.group(2));
}
}else{
System.out.println("None");
}
testCases--;
}
}
}


When inputting:

3
<a>test</a>
<b></b>
<c>test</c>


My output should be:

test
None
test


But instead it is:

test

test


My question is: Why is my if-statement not catching the newline and printing "None"?

Answer

There is no new line, there is just empty string, try to match empty string like this:

if (m.group(2).matches("^$")) {

Or check length of string:

if (m.group(2).length() == 0) {
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