Essential Books

Escape Characters

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Generally

To use regular expression specific characters (?+| etc.) in their literal meaning they need to be escaped. In common regular expression this is done by a backslash \\. However, as it has a special meaning in Java Strings, you have to use a double backslash \\.

These two examples will not work: 

"???".replaceAll ("?", "!"); //java.util.regex.PatternSyntaxException
"???".replaceAll ("\?", "!"); //Invalid escape sequence

This example works 

"???".replaceAll ("\\?", "!"); //"!!!"

Splitting a Pipe Delimited String

This does not return the expected result: 

"a|b".split ("|"); // [a, |, b]

This returns the expected result: 

"a|b".split ("\\|"); // [a, b]

Escaping backslash \\

This will give an error: 

"\\".matches("\\"); // PatternSyntaxException
"\\".matches("\\\"); // Syntax Error

This works: 

"\\".matches("\\\\"); // true
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Regular Expressions:
* Regular Expressions
* Using capture groups
* Using regex with custom behaviour by compiling the Pattern with flags
* Escape Characters
* Not matching a given string
* Matching with a regex literal.
* Matching a backslash
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0 Inheritance
1 Getting started with Java
2 Streams
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4 Collections
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125 Java command: java and javaw
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183 CompletableFuture
184 Contributors