Detailed introduction to single character matching and predefined characters of Java regular expressions-javaTutorial-php.cn

本篇文章给大家带来了关于java的相关知识，其中主要介绍了关于单字符匹配和预定义字符的相关内容，下面一起来看一下，希望对大家有帮助。

Detailed introduction to single character matching and predefined characters of Java regular expressions

一、需求

现有一个字符串，需满足如下要求：

[6, 18] 个字符
只能包含字母、数字、下划线
需以字母开头

如果字符串满足上述要求，返回 true，否则返回 false

   public static boolean validString(String s) {
       return s.matches("[a-zA-Z][a-zA-Z0-9_]{5,17}");
   }

Copy after login

正则表达式用极简的规则取代了复杂的验证逻辑

Regex Expression

正则表达式是一种通用的技术，适用于多种编程语言

二、单字符匹配（6个）

<span style="font-family:Microsoft Yahei, Hiragino Sans GB, Helvetica, Helvetica Neue, å¾®è½¯é›…é»‘, Tahoma, Arial, sans-serif">1. </span>[abc]：字符串的某个位置（某一个字符）满足 a、b、c 中的一个

某个位置：该【单字符匹配】放的位置

public class TestDemo {
    public static void main(String[] args) {
        String regex = "[zgq]";
        System.out.println("z".matches(regex)); // true
        System.out.println("g".matches(regex)); // true
        System.out.println("q".matches(regex)); // true
        System.out.println("zgq".matches(regex)); // false
    }}

Copy after login

public class TestDemo {
    public static void main(String[] args) {
        String regex = "26[abc]3q";
        System.out.println("26a3q".matches(regex)); // true
        System.out.println("26abc".matches(regex)); // false
        System.out.println("26b3q".matches(regex)); // true 
    }}

Copy after login

2. [^abc]：除了 a、b、c 之外的任意单个字符

public class TestDemo {
    public static void main(String[] args) {
        String regex = "[^cat]666";
        System.out.println("c666".matches(regex)); // false
        System.out.println("a666".matches(regex)); // false
        System.out.println("t666".matches(regex)); // false
        System.out.println("bb666".matches(regex)); // false
        System.out.println("b666".matches(regex)); // true
    }}

Copy after login

public class TestDemo {
    public static void main(String[] args) {
        String regex1 = "[12345]666";
        String regex2 = "[^1-5]666";
        System.out.println("1666".matches(regex1)); // true
        System.out.println("3666".matches(regex1)); // true
        System.out.println("5666".matches(regex1)); // true
        System.out.println("6666".matches(regex1)); // false

        System.out.println("1666".matches(regex2)); // false
        System.out.println("3666".matches(regex2)); // false
        System.out.println("5666".matches(regex2)); // false

        System.out.println("6666".matches(regex2)); // true
    }}

Copy after login

3. [a-zA-z]：匹配单个英文字母

public class TestDemo {
    public static void main(String[] args) {
        String regex = "[a-zA-Z]666";
        System.out.println("6666".matches(regex)); // false
        System.out.println("b666".matches(regex)); // true
    }}

Copy after login

4. [a-d[1-6]]：和 [a-d1-6] 一样（并集）

public class TestDemo {
    public static void main(String[] args) {
        String regex1 = "[a-d[1-6]]";
        String regex2 = "[a-d1-6]";
        System.out.println("a".matches(regex1)); // true
        System.out.println("e".matches(regex1)); // false
        System.out.println("1".matches(regex1)); // true
        System.out.println("7".matches(regex1)); // false

        System.out.println("a".matches(regex2)); // true
        System.out.println("e".matches(regex2)); // false
        System.out.println("1".matches(regex2)); // true
        System.out.println("7".matches(regex2)); // false
    }}

Copy after login

5. [zgq&&[god]]：交集

public class TestDemo {
    public static void main(String[] args) {
        String regex1 = "[zgq&&[god]]";
        System.out.println("q".matches(regex1)); // false
        System.out.println("d".matches(regex1)); // false
        System.out.println("g".matches(regex1)); // true
    }}

Copy after login

6. [zgq&&[god]]：取差集

public class TestDemo {
    public static void main(String[] args) {
        String regex1 = "[zgq&&[^god]]";
        System.out.println("q".matches(regex1)); // true
        System.out.println("d".matches(regex1)); // false
        System.out.println("g".matches(regex1)); // false
        System.out.println("z".matches(regex1)); // true

        // 取差集, 从字母 a 到字母 z 中去除字母 b 和 d
        String regex2 = "[a-z&&[^bd]]";
        System.out.println("d".matches(regex2)); // false
        System.out.println("a".matches(regex2)); // true
    }}

Copy after login

三、预定义字符（7个）

预定义字符匹配的仍然是单个字符

【.】：任意单个字符
【\d】：数字
【\D】：非数字
【\s】：空白
【\S】：非空白
【\w】：字母（英文字母、下划线、数字）
【\W】：非英文字母

Java 中需以两个【\】开头表示预定义字符

public class TestDemo {
    public static void main(String[] args) {
        String r1 = ".";
        System.out.println("@".matches(r1)); // true
        System.out.println("庆".matches(r1)); // true
        System.out.println("I".matches(r1)); // true
        System.out.println(" ".matches(r1)); // true
        System.out.println(".".matches(r1)); // true
    }}

Copy after login

public class TestDemo {
    public static void main(String[] args) {
        // 匹配 java 文件
        String r1 = ".\\.java";
        System.out.println("a.java".matches(r1)); // true
        System.out.println("xjava".matches(r1)); // false
        System.out.println("5java".matches(r1)); // false
    }}

Copy after login

public class TestDemo {
    public static void main(String[] args) {
        String r1 = "[abc]";
        String r2 = "\\[abc\\]";
        System.out.println("a".matches(r1)); // true
        System.out.println("c".matches(r1)); // true
        System.out.println("[abc]".matches(r1)); // false

        System.out.println("a".matches(r2)); // false
        System.out.println("c".matches(r2)); // false
        System.out.println("[abc]".matches(r2)); // true
    }}

Copy after login

推荐学习：《java视频教程》

The above is the detailed content of Detailed introduction to single character matching and predefined characters of Java regular expressions. For more information, please follow other related articles on the PHP Chinese website!