Character class subtraction, converting from Java syntax to RegexBuddy

Question

Which regular expression engine does Java uses?

In a tool like RegexBuddy if I use

[a-z&&[^bc]]

that expression in Java is good but in RegexBuddy it has not been understood.

In fact it reports:

Match a single character present in the list below [a-z&&[^bc]

• A character in the range between a and z : a-z
• One of the characters &[^bc : &&[^bc
• Match the character ] literally : ]

but i want to match a character between a and z intersected with a character that is not b or c

Answer 1

Like most regex flavors, java.util.regex.Pattern has its own specific features with syntax that may not be fully compatible with others; this includes character class union, intersection and subtraction:

• [a-d[m-p]] : a through d, or m through p: [a-dm-p] (union)
• [a-z&&[def]] : d, e, or f (intersection)
• [a-z&&[^bc]] : a through z, except for b and c: [ad-z] (subtraction)

The most important "caveat" of Java regex is that matches attempts to match a pattern against the whole string. This is atypical of most engines, and can be a source of confusion at times.

See also

• regular-expressions.info/Flavor Comparison and Java Flavor Notes

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On character class subtraction

Subtraction allows you to define for example "all consonants" in Java as [a-z&&[^aeiou]].

This syntax is specific to Java. In XML Schema, .NET, JGSoft and RegexBuddy, it's [a-z-[aeiou]]. Other flavors may not support this feature at all.

References

• regular-expressions.info/Character Classes in XML Regular Expressions
• MSDN - Regular Expression Character Classes - Subtraction

Related questions

• What is the point behind character class intersections in Java’s Regex?

Answer 2

Java uses its own regular expression engine, which behaviour is defined in the Pattern class.

You can test it with an Eclipse plugin or online.