如何使用单个replaceAll找到Java中两个字符串的共同字符？

import java.util.regex.Pattern;

public class CommonCharacters {
    public static void main(String[] args) {
        String str1 = "hello";
        String str2 = "world";
        String commonChars = findCommonChars(str1, str2);
        System.out.println("共同字符: " + commonChars);
    }

    public static String findCommonChars(String str1, String str2) {
        String commonChars = "";
        for (char c : str1.toCharArray()) {
            String regex = "[" + c + "]";
            if (str2.matches(regex)) {
                commonChars += c;
            }
        }
        return commonChars;
    }
}