如何按收集器对内部类列表进行分组？

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class InnerClassGrouping {
    public static void main(String[] args) {
        // 内部类列表
        List<String> innerClasses = Arrays.asList("ClassA$Inner1", "ClassA$Inner2", "ClassB$Inner1", "ClassB$Inner2");

        // 按收集器对内部类列表进行分组
        Map<String, List<String>> groupedClasses = innerClasses.stream()
                .collect(Collectors.groupingBy(className -> {
                    // 获取内部类的外部类名
                    int dollarIndex = className.indexOf('$');
                    return className.substring(0, dollarIndex);
                }));

        // 打印分组结果
        groupedClasses.forEach((outerClass, innerClassList) -> {
            System.out.println("Outer Class: " + outerClass);
            System.out.println("Inner Classes: " + innerClassList);
            System.out.println();
        });
    }
}

Outer Class: ClassA
Inner Classes: [ClassA$Inner1, ClassA$Inner2]

Outer Class: ClassB
Inner Classes: [ClassB$Inner1, ClassB$Inner2]