java.util.regex.PatternSyntaxException - when using split("\\");

Question

I'm solving this problem in my own way. I'm trying to split the file path into Drive, folders, and file name, all into an array.

The problem:

String regex = "\\";
String [] divisions = path.split (regex);

This gives me an java.util.regex.PatternSyntaxException. I looked up the wiki and found [\b]

String regex = "[\b]";
String [] divisions = path.split (regex);

This doesn't work. It doesn't throw an exception, nor does it split my file path based on backspace.

Input:

► Enter path -- 
C:\User\Admin\NekedGaben.jpg

Output:

→ Path = C:\User\Admin\NekedGaben.jpg
→ File name = C:\User\Admin\NekedGaben
→ Extension = .jpg

My questions:

What is \ in regex? (Not "\\", that is a String literal.) — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Feb 2, 2015 at 17:19
You want to read the wiki more carefully: [\b] matches a backspace, not a backslash. Why would you ever want to match a backspace? I don't know, I've never needed to. But \b by itself matches a word boundary, and it can't mean that inside a character class, so its meaning arbitrarily changes to backspace. — Alan Moore
– Alan Moore, Commented Feb 2, 2015 at 23:11

anubhava · Accepted Answer · 2015-02-02 17:20:10Z

6

You should use double escaping in Java regex, i.e.:

String regex = "\\\\";

Or use static Pattern.quote(String) method:

String regex = Pattern.quote("\\");

answered Feb 2, 2015 at 17:20

anubhava

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Comments

Maroun · Accepted Answer · 2015-02-02 17:23:23Z

2

Because \b is a single character, the compiler knows it, they're friends.

However backslash (\) is represented by \\ in Java, and \ is invalid regex, in order to escape it, you should use:

\\\\
↓ ↓
escaping

Solution:

answered Feb 2, 2015 at 17:21

Maroun

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