如何从另一个方法访问变量

Question

我在Java有个叫"Game"的class，aim/goal是去某个房间，"throne"房间。当到达王座室时游戏结束。

public class Game {

    // fields

    private Room currentRoom;
    private boolean finished;
    private Room throne;

    /**
     * Create the game and initialise its internal map.
     */
    public Game() 
    {
        finished = false;
        createRooms();
    }

    /**
     * Create all the rooms and link their exits together.
     */
    private void createRooms()
    {
        Room gate, graveyard, church, crypt, entrance, hall, kitchen, buttery, greathall, staircase,
        dungeon, topstaircase, throne, solar, wardrobe, privy;

        // create the rooms
        gate = new Room("outside the old gate of the castle");
        graveyard = new Room("on a wind-swept gaveyard");
        church = new Room("in a small ancient church");
        throne = new Room("in the throne room with golden walls");
        // other rooms ...

        // initialize room exits

        gate.setExit("north", graveyard);
        throne.setExit("south", topstaircase);
        // other exits ...
    }
}

进入一个 direction/room :

public String goRoom(String direction) 
{
    assert direction != null : "Game.goRoom gets null direction";

    // Try to leave current room.
    Room nextRoom = currentRoom.getExit(direction);
    if (nextRoom == null) {
        return "There is no exit in that direction!";
    } else {
        currentRoom = nextRoom;
        return currentRoom.getLongDescription();
    }
}

进入特定房间结束游戏，即 "throne" 房间，我是这样做的：

    if (currentRoom.equals(throne)) {
        finished = true;
        return "Congrats you have reached the throne room";
    }

但是我一直收到这个错误：cannot find symbol - variable throne

这是一个基于"Object first with Java using blueJ"

的项目

Answer 1

您可以将其声明为一个字段，而不是在您的 private void createRooms() 中声明 Room 宝座，因此您可以在构造函数之后立即说 Room throne;，然后您仍然可以在 Room throne; 中对其进行初始化=13=]方法。

你可以考虑制作它final因为它不会再改变并且清楚地表明了意图

在这种情况下，我不会将它传递给下一个参数，对我来说，将它作为一个字段是有意义的

编辑：关于您无法访问的声明评论的主题，我怀疑您正在做的是在执行以下代码后检查游戏的完成状态：

} else {
        currentRoom = nextRoom;
        return currentRoom.getLongDescription();
    }

因为您已经从此处的方法返回，所以您从未真正检查过游戏的结束状态。

Answer 2

您正在将 Room 存储为 local 变量。一旦您的方法终止，这些变量就会被删除，因此 Rooms 将消失。

要解决这个问题，您应该在 class 级别声明您的变量：

public class Game {
    private Room currentRoom;
    private boolean finished;
    private Room Goal;
    private Map<String, Room> rooms;


public Game() {
    finished = false;
    rooms = new HashMap<>();
    createRooms();
}

//....

private void createRooms() {
    rooms.put("gate", new Room("outside the old gate at the castle"));
    //similar for other rooms
    //...
}

然后，您可以通过定义一个函数来访问您的房间

public Room getRoom(String roomName) {
    if (rooms.containsKey(roomName))
        return rooms.get(roomName);
    throw new IllegalArgumentException("No such room: " + roomName);
}

例如：

if (currentRoom.equals(getRoom("throne")) {

        finished = true;
        return "Congrats you have reached the throne room";
}

如果goRoom()不在Game中，您需要先获取Game的实例，然后在该实例上调用getRoom()。

Answer 3

But I keep getting this error : "cannot find symbol - variable throne". I believe i need a field somewhere but I am unsure where and how this is useful.

您收到此错误是因为变量 throne 是一个局部变量，其作用域就在声明它的方法内

private void createRooms()
{
    Room gate, graveyard, church, crypt, entrance, hall, kitchen, buttery, greathall, staircase,
        dungeon, topstaircase, throne, solar, wardrobe, privy;


    // create the rooms
    gate = new Room("outside the old gate of the castle");
    graveyard = new Room("on a wind-swept gaveyard");
    church = new Room("in a small ancient church");
    throne = new Room("in the throne room with golden walls");// local variable
    // other rooms ...

    // initialise room exits

    gate.setExit("north", graveyard);
    throne.setExit("south", topstaircase);
    // other exits ...
    }

现在，您可以将其设为 instance variable 或 class variable，这样它就可以访问，而不是将其设为本地，如果您希望将此变量设为 private instance variable，则提供 getter 和setter 来访问这个变量的值。

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