java如何一次退出所有多个嵌套方法

3 月，1 周 Questions & Answers 61

我一直在学习Tim Buchalka为软件开发人员开设的Java编程大师课程，并修改了第118课中的程序

我想在运行时使用列表迭代器（navigate方法）更新列表。程序运行正常，但如果我更新列表，Java会抛出一个错误：ConcurrentModificationException

我提出了以下解决方案：每当用户修改列表时，都会运行其他方法，更新列表并将其传递给navigate（）方法。通过这样做，我的程序将进入多层嵌套方法，当用户想要退出程序时，问题就会出现（案例0:in navigate（）方法）。用户按0的次数与运行嵌套方法的次数相同

我最初的想法是计算navigate（）被嵌套的次数，然后使用for循环返回作为嵌套次数。但后来我明白了这毫无意义

我怎样才能使用case 0:一次退出程序

package com.practice;

import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Scanner;

public class List extends Traveler {
    private LinkedList<String> linkedList;
    private String tripName;


    public List(String travelerName, int travelerAge, String tripName) {//it has to have same amount of parameters or more with super constructor!
        super(travelerName, travelerAge);
        this.tripName = tripName;
        this.linkedList = new LinkedList<>();
    }

    public List(){} //it has to have same amount of parameters or more with super constructor!

    public LinkedList<String> getLinkedList() {
        return linkedList;
    }

    public String getTripName() {
        return tripName;
    }

    private void removeCity(LinkedList<String> cityList, String deletedCity) {
        if(cityList.remove(deletedCity)) {
            System.out.println(deletedCity + " has been removed");
        } else System.out.println("Could not find the city you want to remove");

        List.navigate(cityList);
    }

    //adds a new city and update the list without an error
    private void noExceptionError(LinkedList<String> listOfCities, String cityName) {
        ListIterator<String> listIterator = listOfCities.listIterator();

        while((listIterator.hasNext())) {
            int comparison = listIterator.next().compareTo(cityName);
            if(comparison == 0) {
                System.out.println(cityName + " has been already added to the list");
                return;
            } else if(comparison > 0) {
                listIterator.previous();
                break;
            }
        }
        listIterator.add(cityName);

        List.navigate(listOfCities);
    }


    private void loadToList(LinkedList<String> listOfCities) {
        alphabeticallyAdd(listOfCities, "Poznan");
        alphabeticallyAdd(listOfCities, "Gdansk");
        alphabeticallyAdd(listOfCities, "Szczeczin");
        alphabeticallyAdd(listOfCities, "Warszawa");
        alphabeticallyAdd(listOfCities, "Lodz");
        alphabeticallyAdd(listOfCities, "Wroclaw");

        List.navigate(listOfCities);
    }

    private void alphabeticallyAdd(LinkedList<String> listOfCities, String cityName) {
        ListIterator<String> listIterator = listOfCities.listIterator(); //just a setup; doesn't point to the 1st element

        while((listIterator.hasNext())) {
            //if value is greater, the word that is in the list is alphabetically bigger, thus, put it before the list element
            //if equal, it is duplicate! return false
            // else it is less, thus, we have to move further in the list
            int comparison = listIterator.next().compareTo(cityName); //retrieves the 1st value and goes to the next
            if(comparison == 0) {
                System.out.println(cityName + " has been already added to the list");
                return;
            } else if(comparison > 0) {
                listIterator.previous(); //because we've used .next() in the int comparison initialization
                listIterator.add(cityName); //don't use linkedList.add because it doesn't know the int comparison, so cannot properly add!!!
                return;
            }
        }
        listIterator.add(cityName); //adding at the end of the list
    }

    public static void navigate(LinkedList<String> listOfCities) {
        Scanner userChoice = new Scanner(System.in);
        List travelListObject = new List();

        ListIterator<String> listIterator = listOfCities.listIterator();
        boolean goingForward = true;

        while(true) {
            Main.menu();
            int choice = userChoice.nextInt();
            userChoice.nextLine(); //takes care of enter key problem
            switch(choice) {
                case 0:
                    System.out.println("Goodbye");
                    //possible improvement
/*                    for(int i = 0; i <= List.amountNestedMethods; i++) {
                        return;
                    }*/
                    return;
                case 1: //moving forward
                    if(!goingForward) {
                        if(listIterator.hasNext()) {
                            listIterator.next();
                        }
                    }
                    if(listIterator.hasNext()) {
                        System.out.println(listIterator.next());
                        Traveler.setNumberVisitedCities(Traveler.getNumberVisitedCities() + 1);
                        goingForward = true;
                    } else {
                        System.out.println("No more cities in the list");
                        goingForward = false;
                    }
                    break;
                case 2: //moving back
                    if(goingForward) {
                        if(listIterator.hasPrevious()) {
                            listIterator.previous();
                        }
                        goingForward = false;
                    }
                    if(listIterator.hasPrevious()) {
                        Traveler.setNumberVisitedCities(Traveler.getNumberVisitedCities() + 1);
                        System.out.println(listIterator.previous());
                    } else {
                        System.out.println("You're at the beginning of the list");
                        goingForward = true;
                    }
                    break;
                case 3:
                    Main.printCities(listOfCities);
                    break;
                case 4:
                    break;
                case 5:
                    System.out.println("Write new city");
                    String addedCity = userChoice.next();
                    travelListObject.noExceptionError(listOfCities, addedCity);
                    break;
                case 6:
                    System.out.println("Write the city you want to delete");
                    String deletedCity = userChoice.next();
                    travelListObject.removeCity(listOfCities, deletedCity);
                    break;
                case 7:
                    System.out.println("You have been in " + Traveler.getNumberVisitedCities() + " cities in total");
                    break;
                case 9:
                    travelListObject.loadToList(listOfCities);
                    break;
                default:
                    System.out.println("Something weird happened. Try to choose an option again");
            }
        }
    }
}

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