Java Basics-Regular expressions

Getting Started with regular expressions

Str.matches ("\\d+"); Returns true from 1 to multiple digits

What is a regular expression? is a string, a string consisting of a meta-character "pre-defined character" and a normal character and quantifier.

What is the function of regular expressions? Used to implement matching or filtering of strings.

The meta-characters of the regular expression are as follows:

\d Number (digit)

\d Non-digital

\s Spaces (space)

\s Non-whitespace

\w single character: a symbol in an alphanumeric underline (word)

\w non-single-character: a symbol outside of single-character

. An arbitrary character [except \ n \ r]

^regex$ ^ means start $ means end

| Or

The quantifiers are as follows:

+ 1 or more characters

* 0 or more characters

？ 0 or 1 characters

{n} exactly n characters

{N,} at least n characters

{n,m} at least N, up to M characters

Character:

Use [] to list the characters that appear

[Ac?_6] represents one of 5 characters

[0-9] represents one of the 0-9,-Indicates the range

So \w is equivalent to [a-za-z0-9_]

Regular applications:

Common methods for the regular correlation of string classes

Boolean matches (regex); match : match strings according to regular requirements

String[] Split (regex); split : Splits a string according to regular requirements

Split Example:

String str= "I love! You? ";

String regex= "[\\s!? \\d]{1,} "; One or more spaces and exclamation marks, question mark, number

String[] S=str.split (regex);

for (String tem:s) {

println (TEM);

}

println ("number" +s.length);

Accumulation:

Non-negative integer [0-9]+

positive integers [1-9]\\d* OR [1-9][0-9]*

After the beginning of the letter, follow 3-6 arbitrary characters [a-za-z]. {3,6} equivalent [A-za-z]{1}. {3,6}

Replace

String newstr = Str.replaceall (string regex,string replament); Replace Regex with Replament

Accumulation:

Or, either the NBA or the CBA:NBA|CBA.

Phone number: [1][3578][0-9]{9}

Email: [Email protected]+[.]. + is wrong [a-za-z0-9]\\w*[@][a-za-z0-9]+[.] [A-za-z] {2,3}

Example:

Java.util.Pattern

Pattern.matches (Regex,email); Equivalent to Email.matches (regex);

Filter

Not to be continued

Java Basics-Regular expressions