CODEWITHSUNDEEP
javaarraysregex
James
James

Reputation: 338

Java Regex error/issue (what kind of character is [ )?

I am trying to write an array to a text file, and in the process I have noticed that arrays are written in the format of: [1, 1, 2, 2] (an example of an int array) and I want to convert an array, take the int array above as an example, convert it to a string and remove the [ and , from it. How can I go about doing it, I've tried looking for a string pattern I could write and had no luck, I have also tried writing:

char [] PIN = System.console().readPassword();
    String pin = java.util.Arrays.toString(PIN);
    String WriteToF = pin.replaceAll("[", "");

but get the following error:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed char
acter class near index 0
[
^
    at java.util.regex.Pattern.error(Unknown Source)
    at java.util.regex.Pattern.clazz(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.replaceAll(Unknown Source)

Also what kind of a character is [ classed as in Java in terms of These patterns?

Upvotes: 0

Views: 70

Answers (3)

Avinash Raj
Avinash Raj

Reputation: 174776

In regex [ is considered as a special meta character(start of a charcter class). To match a literal [, you need to escape [ symbol when passing it to replaceAll function.

String WriteToF = pin.replaceAll("\\[", "");

When the regex engine see a [ character then it considered it as a start of a character class. If a character class is opened then it must be closed using ](] means the end of character class.).

so that only you get the below error.

Unclosed character class near index 0

Upvotes: 0

Jiang
Jiang

Reputation: 588

  1. use replaceAll("\\[", "") instead.
  2. [ is to represent the beginner of Character classes, which need to be escaped when matching [ literally.

Upvotes: 0

August
August

Reputation: 12558

The String#replaceAll method replaces using regex. If you want to replace the literal [ character, you should use the String#replace method:

String WriteToF = pin.replace("[", "");

In regex, the [ character marks the beginning of a character class. You need to close the character class with ] for it to be valid regex syntax. If you wanted to replace the literal [ character with regex, you would escape it: "\\[".

Upvotes: 2

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