使用正则表达式可以尝试：

String input = "fliM8fLam";
String output = input.replaceAll("(?<=\\D)(?=\\d)|(?<=\\d)(?=\\D)|(?<=[a-z])(?=[A-Z])|(?<=[A-Z])(?=[a-z])", "-");
System.out.println(output);  // fli-M-8-f-L-am

1.您可以使用[^\\p{Alnum}]检查非字母数字字符。了解有关documentation模式的更多信息。
1.您可以使用[a-z]+(?=[A-Z\d])|[A-Z]+[a-z]+|\d+|[A-Z]获取匹配组。从this demo了解有关此模式的更多信息。您可以使用常规循环或Stream API连接匹配组，如以下演示所示。

• • 演示**：

import java.util.regex.MatchResult;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

class Main {
    public static void main(String[] args) {
        // Test
        String[] arr = {
                "flimFlam",
                "fliMflam",
                "fliM8fLam",
                "flim$Flam"
        };
        for (String s : arr) {
            try {
                System.out.println("Trying to hyphenate " + s);
                System.out.println(hyphenate(s));
            } catch (IllegalArgumentException e) {
                System.out.println(e.getMessage());
            }
        }
    }

    public static String hyphenate(String input) {
        if (Pattern.compile("[^\\p{Alnum}]").matcher(input).find()) {
            throw new IllegalArgumentException("Illegal!");
        }

        String regex = "[a-z]+(?=[A-Z\\d])|[A-Z]+[a-z]+|\\d+|[A-Z]";
        return Pattern.compile(regex)
                .matcher(input)
                .results()
                .map(MatchResult::group)
                .collect(Collectors.joining("-"));
    }
}

• • 输出**：

Trying to hyphenate flimFlam
flim-Flam
Trying to hyphenate fliMflam
fli-Mflam
Trying to hyphenate fliM8fLam
fli-M-8-f-Lam
Trying to hyphenate flim$Flam
Illegal!