如何从另一个类访问arraylist，该类的主要用途不是arraylist

Question

我已经阅读了一页又一页的stackoverflow，试图解决我的问题，并多次修改代码，但都无济于事。我希望我能简化我的问题，但我不能完全确定我的代码中出了什么问题。

我正在为我正在学习的课程创建一个游戏。到目前为止，代码涉及一个生物的父类，以及生物类型(动物、鼻咽癌等)的子类，它们是加载的房间，另一个类。我已经创建了一个SAXParser来解析包含每个生物和房间的详细信息的xml文件，以便用每个房间中的房间和生物填充游戏。我对当前分配的检查是，当用户给出它想要查看的房间的名称时，打印出给定房间的内容。房间都放在roomArrayList里。我已经创建了一个主类，它负责处理用户输入。

房间里塞满了合适的东西。当我在解析器中设置"EndElement“方法以打印刚创建的房间的内容时，输出是正确的。

但是，当我尝试根据用户从主类发出的请求使用roomArrayList打印其中一个房间的内容时，我得到了异常。我使用get方法将数组导入到主类中，如下所示。我可以判断出有问题，因为当我打印导入数组的大小时，它打印的是零。

我不会费心去包括生物父类和子类。

下面是MyHandler类：

public class MyHandler extends DefaultHandler {

    private List<Room> roomList = null;
    private Room r;
    private PC pc;
    private String south, north, west, east;


    ArrayList<Room> roomArrayList = new ArrayList<Room>();

    public ArrayList<Room> getArrayList() {
        return roomArrayList;
    }

    public int checkRoomMatch(String match) {
        int a = -1;
        for (int i = 0; i < roomArrayList.size(); i++) {
            if (roomArrayList.get(i).RoomName.equals(match)) {
                a = i;
            }
        }
        return a;
    }

    public void startDocument() {
        System.out.println("Document parsing started.");
    }

    @Override
    public void startElement(String uri, String localName, String
            qName, Attributes attributes) {

        if (qName.equals("room")) {
            r = new Room(attributes.getValue("name"));
            r.setDescription(attributes.getValue("description"));
            r.setState(attributes.getValue("state"));
            north = attributes.getValue("north");
            west = attributes.getValue("west");
            east = attributes.getValue("east");
            south = attributes.getValue("south");

            r.setNeighbor(south, north, east, west, roomArrayList);

            roomArrayList.add(r);
        }
        else if (qName.equals("animal")) {
            Animal animal = new Animal
                    (attributes.getValue("name"), attributes.getValue("description"),
                            r, qName);
            r.addCreature(animal);
        }
        else if (qName.equals("NPC")) {
            NPC npc = new NPC(attributes.getValue("name"),
                    attributes.getValue("description"), r, qName);
            r.addCreature(npc);
        }
        else if (qName.equals("PC")) {
            pc = new PC(attributes.getValue("name"),
                    attributes.getValue("description"), r, qName);
            r.addCreature(pc);
        }
    }

    public void endElement(String uri,
                           String localName,
                           String qName) {

        if (qName.equals("room")) {
            System.out.println(r.toString());
        }
    }

    public void endDocument() {
        System.out.println("Document parsing ended.");
    }
}

这是我的Room类：

public class Room {

    Creature[] CreatureArray = new Creature[10];
    String RoomName;
    private int CreatureCount = 0;
    String description;
    String currentState;
    final String Dirty = "dirty";
    final String HalfDirty = "half-dirty";
    final String Clean = "clean";

    // 0 is north, 1 is east, 2 is south, 3 is west
    private Room[] roomArray = new Room[4];

    public Room(String name) {
        RoomName = name;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public void setState(String state) {
        this.currentState = state;
    }

    public String getName() {
        return RoomName;
    }

    public String toString() {
        String roomInfo = "";
        roomInfo += "This room is called" + RoomName + "." + "\n";
        roomInfo += "The following animals are in this room: ";
        for (int x = 0; x < CreatureCount; x++) {
            roomInfo += CreatureArray[x].toString();

            if (x < CreatureCount - 1) {
            }
        }

        roomInfo += "\n" + "The description for room " + RoomName + " is: 
        " + description + ". " + "\n ";
        roomInfo += "The current state of room " + RoomName + " is " +
                currentState + "." + "\n";
        roomInfo += "Room " + RoomName + " is positioned with room " +
                "roomArray[0]" + " to the north, room "
                + "roomArray[1]" + " to the east, room " + "roomArray[2]"
                + " to the south and room "
                + "roomArray[3]" + " to the west." + "\n";

        return roomInfo;
    }

    public void addCreature(Creature a) {
        if (CreatureCount < 10) {
            CreatureArray[CreatureCount] = a;
            CreatureCount++;
        }
        else {
            System.out.println("This room is full.");
        }
    }

    public void setNeighbor(String south, String north, String east,
                            String west, ArrayList<Room> roomArrayList) {

        if (roomArrayList.size() >= 1) {
            for (int i = 0; i < roomArrayList.size(); i++) {
                if (roomArrayList.get(i).RoomName.equals(north)) {
                    roomArray[0] = roomArrayList.get(i);
                    roomArrayList.get(i).roomArray[2] = this;
                    continue;
                }

                if (roomArrayList.get(i).RoomName.equals(south)) {
                    roomArray[2] = roomArrayList.get(i);
                    roomArrayList.get(i).roomArray[0] = this;
                    continue;
                }

                if (roomArrayList.get(i).RoomName.equals(east)) {
                    roomArray[1] = roomArrayList.get(i);
                    roomArrayList.get(i).roomArray[3] = this;
                    continue;
                }

                if (roomArrayList.get(i).RoomName.equals(west)) {
                    roomArray[3] = roomArrayList.get(i);
                    roomArrayList.get(i).roomArray[1] = this;
                    continue;
                }
            }
        }
    }
}

下面是处理用户输入的main方法。我已经注释掉了打印导入数组大小的命令。但请记住，当运行这行代码时，输出为零。下面的println命令应该是打印所选房间内容的函数。

public class Main {

    public static void main(String[] a) throws Exception {
        File f;
        Scanner fs = null;

        Scanner kb = new Scanner(System.in);
        System.out.println("Enter a file name:");

        String fileName = kb.nextLine();

        f = new File(fileName);

        if (!f.exists()) {
            System.out.println("File not found. Please try again.");
            System.out.println("Enter a file name:");
        }

        SAXParserFactory factory = SAXParserFactory.newInstance();

        MyHandler handler = new MyHandler();
        SAXParser saxParser = factory.newSAXParser();
        saxParser.parse(fileName, new MyHandler());

        System.out.println("Enter the name of a room for which you would " +
                "like to see the contents.");

        String selectedRoom = kb.nextLine();

        ArrayList<Room> roomArrayList = handler.getArrayList();

        int roomIndex = handler.checkRoomMatch(selectedRoom);
        while (roomIndex == -1) {
            System.out.println("No such room existed in the input file.");
            System.out.println("Enter the name of a room for which you " +
                    "would like to see the contents.");
            selectedRoom = kb.nextLine();

            roomIndex = handler.checkRoomMatch(selectedRoom);
        }
        //        System.out.println(roomArrayList.size());
        System.out.println(roomArrayList.get(roomIndex).toString());
    }
}

我希望我已经正确地创建了这个问题。这是我第一次提出问题，因为我真的觉得我已经耗尽了我的资源。

tl;dr --为什么填充的roomArrayList没有导入到我的main方法中？

Answer 1

您正在向解析器传递一个新的MyHandler实例，在该实例中，数组列表将被填充，而不在现有的处理程序实例中，因此它保持为空。

因此，不是传递新的处理程序，而是使用现有的处理程序，如：

saxParser.parse(fileName, new MyHandler());

使用：

saxParser.parse(fileName, handler);//now handler will be having array list populated with rooms and you could use it further.