Java Greenfoot，无法链接文件之间的方法

Question

在学校做一个项目，我是编程的初学者，我在制作泡泡射手时遇到了很大的问题，我需要在它变成map2之前得到地图上所有的球。

试图列出所有的球，但程序在第一个地图的末尾崩溃，并给我们错误报告，它无法加载负值。我认为是在它试图给枪装弹的时候，并且想要放一条if -语句，如果"allowedBallTypes != null“或零，那么它就应该给枪装弹。

找不到symbol - getAllowedBallTypes()；greenfoot java方法类

bubbleworld类：

public BubbleWorld() 
{    
        super(Map.MAX_WIDTH*Map.COLUMN_WIDTH, Map.MAX_HEIGHT*Map.ROW_HEIGHT, 1,false); 

        // Max speed. We use time-based animation so this is purely for smoothness,
        // because Greenfoot is plain stupid. I can't find a way to get 60 Hz so this is
        // what we have to do. Note: Exporting the game seems to cap this to some value < 100. :(
        Greenfoot.setSpeed(100);

        // Load the map.
        map = new Map(this, testMap1);

        // Update the allowed ball types. (i.e. we don't want to spawn a
        // certain color of balls if the map doesn't contain them!)
        map.updateAllowedBallTypes();

        // Create the cannon.
        Cannon cannon = new Cannon();
        addObject(cannon, getWidth()/2, getHeight());

映射类：

       public int[] getAllowedBallTypes()
    {
        return allowedBallTypes;
    }


public void updateAllowedBallTypes()
    {
        int allowedCount = 0;
        boolean[] allowed = new boolean[Ball.typeCount];

        // Only ball types that exist in the map RIGHT NOW as attached balls will be allowed.
        for(Cell c : cells)
        {
            if(c != null && c.getBall() != null && c.isAttached())
            {
                int type = c.getBall().getType();

                if(!allowed[type])
                    allowedCount++;

                allowed[type] = true;
            }
        }

        allowedBallTypes = new int[allowedCount];
        int writeIndex = 0;
        for(int type = 0; type < Ball.typeCount; ++type)
        {
            if(allowed[type])
            {
                allowedBallTypes[writeIndex++] = type;
            }
        }
    }

Cannon类：

private void prepareBall()
    {
        // Get a random ball type from the list of allowed ones. Only balls currently in the map
        // will be in the list.
        int[] allowedBallTypes = ((BubbleWorld)getWorld()).getMap().getAllowedBallTypes();
        int type = allowedBallTypes[Greenfoot.getRandomNumber(allowedBallTypes.length)];

        // Create it and add it to the world.
        ball = new Ball(type);
        getWorld().addObject(ball, getX(), getY());
    }

Answer 1

假设您在Cannon类的粘贴代码片段中收到了该错误，该错误表明BubbleWorld的getMap()方法存在问题--您能粘贴它以便我们可以看到它吗？它可能没有返回正确的类型。通常，您需要粘贴更多的代码，包括完整的类，并指出错误发生的确切位置。一种更简单的方法可能是将您的场景和源代码上传到Greenfoot网站(www.greenfoot.org --使用greenfoot中的共享功能，并确保勾选源代码框)，并提供指向该网站的链接。

Answer 2

根据您的代码，您的映射类似乎没有int[] allowedBallTypes的类级变量声明；