Java Stream - 如何将您自己的方法分配给功能接口

public class Main {
  public static void main(String... args) {
    Something something = new Something();

    Converter<String, String> stringConverter = something::startsWith;
    String converted3 = stringConverter.convert("Java");
    System.out.println(converted3);    // result J
  }
}
class Something {
  String startsWith(String s) {
      return String.valueOf(s.charAt(0));
  }
}
@FunctionalInterface
interface Converter<F, T> {
    T convert(F from);
}