Fix: java.util.regex.PatternSyntaxException

Code:

package org.code2care.example;

public class PatternSyntaxExceptionExample {

    public static void main(String[] args) {

        String string = "1(2(3(4(5";
        String[] strArr = string.split("(");
        
    }
}

Exception:

Exception in thread "main" java.util.regex.PatternSyntaxException: Unclosed group near index 1
(
	at java.base/java.util.regex.Pattern.error(Pattern.java:2028)
	at java.base/java.util.regex.Pattern.accept(Pattern.java:1878)
	at java.base/java.util.regex.Pattern.group0(Pattern.java:3053)
	at java.base/java.util.regex.Pattern.sequence(Pattern.java:2124)
	at java.base/java.util.regex.Pattern.expr(Pattern.java:2069)
	at java.base/java.util.regex.Pattern.compile(Pattern.java:1783)
	at java.base/java.util.regex.Pattern.<init>(Pattern.java:1430)
	at java.base/java.util.regex.Pattern.compile(Pattern.java:1069)
	at java.base/java.lang.String.split(String.java:3151)
	at java. base/java.lang.String.split(String.java:3197)
	at org.code2care.example.JavaSplitOnDotStringExample2.main(JavaSplitOnDotStringExample2.java:7)

Reason for the exception:

The java.lang.String split() function throws a PatternSyntaxException if the if the regular expression's syntax is invalid.

If you take a closer look at the regular expression used here open braces (, this has a special meaning when working with Regular Expressions. Such characters need to be escaped with a double forward slash \\

Fix:

Change the regex string from,

string.split("(");

to,

string.split("\\(");

Below is the list of all the characters that when you want to use "literally" in the regex string needs to be escaped.

Character	Description
\	Escape character
.	Any character except a newline
+	One or more occurrences
*	Zero or more occurrences
?	Zero or one occurrence
`	`
(	Start of a capturing group
)	End of a capturing group
[	Start of a character class
]	End of a character class
{	Start of a quantifier
}	End of a quantifier
-	Range of characters in a class
^	Start of a string/line
$	End of a string/line

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