string.parse("(") error

Question

I have a file which contains data as follows:

recv(1178884, NULL, 4294967267, 0)      = 0 ...... ...... 

My source code is:

try (BufferedReader br = new BufferedReader(new FileReader("D:\\smsTrace.txt"))) {     String sCurrentLine;      while ((sCurrentLine = br.readLine()) != null) {         String sysCallName = sCurrentLine;         String[] sysCallTokens = sysCallName.split("(");         System.out.println(sCurrentLine);     } } catch (IOException e) {     e.printStackTrace(); }  

When I split with sysCallName.split(",") it works fine but when I use as above, it throws following exception.

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed group near index 1 (  ^     at java.util.regex.Pattern.error(Unknown Source)     at java.util.regex.Pattern.accept(Unknown Source)     at java.util.regex.Pattern.group0(Unknown Source)     at java.util.regex.Pattern.sequence(Unknown Source)     at java.util.regex.Pattern.expr(Unknown Source)     at java.util.regex.Pattern.compile(Unknown Source)     at java.util.regex.Pattern.<init>(Unknown Source)     at java.util.regex.Pattern.compile(Unknown Source)     at java.lang.String.split(Unknown Source)     at java.lang.String.split(Unknown Source)     at fileReading.main(fileReading.java:19) 

Any idea what I am doing wrong?

Answer 1

You have to escape the opening bracket:

sysCallName.split("\\("); 

Because split() expects a regular expression, and brackets are used to mark capturing groups in a regex. So they need to be in pairs. If you just want a bracket it needs to be escaped.

Answer 2

String#split takes a regular expression as splitting criteria. Now, ( in regex is used for capturing groups, so you need to escape it, if you want to match it.

You have two ways: -

1. Escape the bracket: -

   sysCallName.split("\\("); 

2. Use Character class: -

   sysCallName.split("[(]"); 

In a character class, all the meta-characters, loose their special meaning, so a ( is just a (, and a dot(.) is just a dot(.). Personally, I prefer the 2nd option, as it looks more clear.