A brief introduction to metacharacters and ordinary characters of java regular expressions

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I. Common characters:

Most characters can only describe themselves and are called ordinary characters, such as all letters and numbers.

That is, ordinary characters can only match characters that are identical to them in a string.

II. Metacharacters:

Because ordinary characters can only match characters that are the same as themselves, the flexibility and powerful matching function of regular expressions cannot be fully displayed, so a series of special characters are specified in regular expressions. These characters are not matched according to the direct quantity of characters, but have special semantics.

For example, the following characters:

^ $ . * + ? = ! : | \ / ( ) [ ] { }

Although the above characters have special meanings, some characters have special meanings only in certain contexts.

If you want to match these character literals with special meaning, you need to put a backslash (\) escape before these characters, for example, I want to match a $literal, I need to write\$, otherwise I match an end position. It is because of these special characters that regular expressions are powerful.

They are called metacharacters because they are the basic characters for constructing regular expressions that match complex text.

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