String.split returning null when using a dot

Question

I got this simple code:

String ip = \"1.2.3.4\";
String[] ipArray = ip.split(\".\");
System.out.println(ipArray[1]);

And ipArray

Answer 1

Pattern.quote(String) can also be used to quote the whole string. This returns a pattern which will be interpreted literally, special characters will have no special meaning. This might be overkill in this case, but sometimes it can be useful.

Answer 2

Use ip.split("\\."); and your problems will be solved. The problem is that String#split receives a regular expression, the dot (.) symbol is a special character in regular expressions, so you need to escape it for it to be interpreted as a plain dot, also as the backslash is an escape character in Java, you have to escape it too.

Answer 3

. is a special character in regular expressions, which is what is used to split a string.

To get around this, you need to escape the .. That leads us to \. Unfortunately, \ is ALSO a special character in the java string, so that must also be escaped, to make \\.

Our "final" result is ip.split("\\.");

In a related issue, the whole process can be averted entirely. There's no sense in doing something that a standard library already has done for us.

Consider the following

byte[] ipOctets = InetAddress.getByName(ip).getAddress();

The only issue here is to remember that if you want the int value, you have to extract it with & like int octet = ipOctets[0] & 0xFF;