How to do dynamic method substitution?

Question

Java

Hello. How to do dynamic method substitution?

Object method = Ticket::getFrom;

if (prop == Properties.FROM) {
    //    method = Ticket::getFrom;
} else if (prop == Properties.TO) {
    //    method = Ticket::getTo;
}

// Как правильно динамически подставлять выражение?
//        return tickets.stream()
//                .collect(Collectors.groupingBy(method,
//                        Collectors.mapping(Function.identity(), Collectors.toList())));

package main.java;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

enum Properties {
    FROM, TO,
}

public class Solution {

    public Map<String, List<Ticket>> fromEntries(List<Ticket> tickets, Properties prop) {

        /*
        return tickets.stream()
                .collect(Collectors.groupingBy(Ticket::getFrom, Collectors.mapping(Function.identity(), Collectors.toList())));

         */
        
//        Object method = Ticket::getFrom;

        if (prop == Properties.FROM) {
//            method = Ticket::getFrom;
        } else if (prop == Properties.TO) {
//            method = Ticket::getTo;
        }

//        return tickets.stream()
//                .collect(Collectors.groupingBy(method,
//                        Collectors.mapping(Function.identity(), Collectors.toList())));
    }

    public List<Ticket> sortingTickets(List<Ticket> tickets) {

        Map<String, List<Ticket>> mapFrom = fromEntries(tickets, Properties.FROM);
        System.out.println(fromEntries(tickets, Properties.FROM));

        return tickets;
    }
}

class Ticket {

    private String from;

    private String to;

    public Ticket(String from, String to) {
        this.from = from;
        this.to = to;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public String getTo() {
        return to;
    }

    public void setTo(String to) {
        this.to = to;
    }

    @Override
    public String toString() {
        return "Ticket{" +
                "from='" + from + '\'' +
                ", to='" + to + '\'' +
                '}';
    }
}

class Main {

    public static void main(String[] args) {

        List<Ticket> tickets = new ArrayList<>();

        Ticket ticket1 = new Ticket("С.Петербург", "Минск");
        Ticket ticket2 = new Ticket("Киев", "Новосибирск");
        Ticket ticket3 = new Ticket("Череповец", "Москва");
        Ticket ticket4 = new Ticket("Минск", "Киев");
        Ticket ticket5 = new Ticket("Москва", "С.Петербург");

        tickets.add(ticket1);
        tickets.add(ticket2);
        tickets.add(ticket3);
        tickets.add(ticket4);
        tickets.add(ticket5);

        System.out.println(new Solution().sortingTickets(tickets));
    }
}

Answer 1

Oh, js is immediately visible. First, you put a normal ide, namely an idea. Then you select Ticket::getTo and press options + commands + m on the poppy, and you substitute the idea for the type. In your case, Function "angle bracket" Ticket, String "angle bracket", and never an object. And in general, everything