JAVA正则表达式

```java
String regex = "\\d+"; // 匹配一个或多个数字
String input = "12345";
boolean isMatch = Pattern.matches(regex, input);
System.out.println(isMatch); // 输出：true
```

```java
String regex = "\\b\\w{3}\\b"; // 匹配长度为3的单词
String input = "Java is a programming language";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
    System.out.println(matcher.group()); // 输出：Java is language
}
```

```java
String regex = "\\d+"; // 匹配一个或多个数字
String input = "I have 123 apples and 456 oranges";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(input);
String result = matcher.replaceAll("X");
System.out.println(result); // 输出：I have X apples and X oranges
```

```java
import java.util.regex.*;
 
public class EmailValidator {
    public static boolean isValid(String email) {
        String regex = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(email);
        return matcher.matches();
    }
 
    public static void main(String[] args) {
        String email1 = "example@mail.com";
        String email2 = "invalid_email.com";
        
        System.out.println(email1 + " is valid: " + isValid(email1)); // 输出：true
        System.out.println(email2 + " is valid: " + isValid(email2)); // 输出：false
    }
}
```