CODEWITHSUNDEEP
javaregexstring
java_guy
java_guy

Reputation: 81

java - String.replaceAll to replace all characters not in pattern

I have a Java regex: 

^[a-zA-Z_][a-zA-Z0-9_]{1,126}$

It means:

Now, I want to replace a string having characters not in that regex with a underscore.

Example:

final String label = "23_fgh99@#";
System.out.println(label.replaceAll("^[^a-zA-Z_][^a-zA-Z0-9_]{1,126}$", "_"));

But the result is still 23_fgh99@#.

How can I "convert" it to _3_fgh99__?

Upvotes: 4

Views: 4526

Answers (1)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626903

Use this code:

final String label = "23_fgh99@#";
System.out.println(label.replaceAll("^[^a-zA-Z_]|(?<!^)[^a-zA-Z0-9_]", "_"));

It outputs _3_fgh99__.

To remove what is "not in the original pattern", you need to negate the first character class and only check a character at the beginning (^[^a-zA-Z_]), and then check other characters not at the beginning with the negated second character class ((?<!^)[^a-zA-Z0-9_]). Then, we just use an alternation symbol | to apply both patterns in 1 replacement operation.

Upvotes: 4

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