在java字符串中替换正则表达式

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args) {
        String input = "Hello, world!";
        String regex = "world";
        String replacement = "Java";

        String output = input.replaceAll(regex, replacement);
        System.out.println(output);
    }
}