Java，访问ArrayList的ArrayList元素

我确实看过，但我想在我的案例中有一个更简单的答案。还研究了似乎可以解释潜在的cast问题，但不能帮助我了解这里的最佳方法。谢谢你花时间阅读这篇文章

最终，我是一名Java新手，我只是想用读入数据结构的基于文本的二维映射实现一个映射类。因为我在阅读之前不知道地图的大小，所以我尝试了向量，但转到了ArrayList

编辑这里的“地图”

我在方法之外，就在类声明下面：

// we have this vector here to be accessible to all methods
// the inner vector will be built in the readMapFile method
static private ArrayList mapList = new ArrayList();

然后在readMapFile方法中（整个方法在末尾）：

在我尝试运行它之前，不会出现错误：

public static char getTerrainAtLocation( int row, int column )
{

    char[] innerList = (char[])mapList.get(row);
    return innerList[column];
}

我显然需要一些帮助！您的最佳建议是什么，我只想从“map”返回x行和y列的字符。我得到以下错误：

Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList cannot be cast to [C
at adventure2.Map.getTerrainAtLocation(Map.java:144)
at adventure2.Map.printMapList(Map.java:154)
at adventure2.Map.main(Map.java:56)
Java Result: 1

这是我完整的readMapFile：

public static void readMapFile( String arg )
{
    if ( arg != "")
    {
        try
        {
            // open a path to the file given in arg 0, this won't throw
            // an exception
            Scanner fileIn = new Scanner(Paths.get(arg));

            // need to clear mapVector for the new file, if it already
            // has data in it
            mapList.clear();

            // this is the line that will throw the exception
            // try to read the file, see if it throws IOException
            mapRows = fileIn.nextInt();
            mapCols = fileIn.nextInt();

            // read to the end of line
            String mapFileLine = fileIn.nextLine();

            // now we have the first line read, with rows and columns
            // need a 2-D char array to hold the map
            //char[][] mapArray = new char [mapRows][mapCols];

            // make up the row vectors row by row, when a row is complete,
            // add that to the full Vector, making a Vector of Vectors

            for ( int i = 0; i < mapRows ; ++i)
            {
                // read each subsequent line in the file
                mapFileLine = fileIn.nextLine();

                ArrayList mapRowList = new ArrayList();

                for ( int j = 0 ; j < mapCols ; ++j )
                {
                    // read each character on the line
                    mapRowList.add(mapFileLine.charAt(j));
                }

                // now put mapRowVector as an element of mapVector
                mapList.add(mapRowList); 

                System.out.println(mapList.get(i));

            }
        }
        catch ( IOException e )
        {
            System.out.println("There was an error reading the file sorry!");
        }
    }
    else
    {
        // arg length was 0 or negative
        System.out.println("Must call readMapFile with a filename as argument");
    } 
} // end readMapFile

公共静态void readMapFile（字符串arg）
{
如果（arg！=“”）
{
尝试
{
//打开arg 0中给定文件的路径，这不会引发
//例外
Scanner fileIn=new Scanner（path.get（arg））；
//需要清除新文件的mapVector（如果已清除）
//里面有数据
clear（）；
//这是将引发异常的行
//尝试读取该文件，看看它是否引发IOException
mapRows=fileIn.nextInt（）；
mapCols=fileIn.nextInt（）；
//读到最后一行
字符串mapFileLine=fileIn.nextLine（）；
//现在我们有了第一行read，包括行和列
//需要一个二维字符数组来保存地图
//char[][]mapArray=new char[mapRows][mapCols]；
//当一行完成时，逐行生成行向量，
//将其添加到完整向量，生成一个向量向量
对于（int i=0；i

---

谢谢

Java的数据结构很棒，但你必须记住最基本的：）

---

FWIW我把地图文本放在上面你到处都在使用原始类型，你应该使用类型参数。八月，我几乎不明白，你指的是调用ArrayList模板时会发生什么？我知道一些C++，但对java有新的认识。1）泛型的原始类型每次都会把你引向这个兔子洞。具体键入

ArrayList

。2） 您正在尝试执行

ArrayList

？

mapList.get（row）

不会返回

ArrayList

。它返回存储在该索引中的

ArrayList

元素。谢谢，我太新了，无法对此进行更新投票。非常酷，它应该是Java中的高级编程类（后C#和C++），但我从未想过使用字节数组，这很酷！）

public static char getTerrainAtLocation( int row, int column )
{

    char[] innerList = (char[])mapList.get(row);
    return innerList[column];
}

Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList cannot be cast to [C
at adventure2.Map.getTerrainAtLocation(Map.java:144)
at adventure2.Map.printMapList(Map.java:154)
at adventure2.Map.main(Map.java:56)
Java Result: 1

public static void readMapFile( String arg )
{
    if ( arg != "")
    {
        try
        {
            // open a path to the file given in arg 0, this won't throw
            // an exception
            Scanner fileIn = new Scanner(Paths.get(arg));

            // need to clear mapVector for the new file, if it already
            // has data in it
            mapList.clear();

            // this is the line that will throw the exception
            // try to read the file, see if it throws IOException
            mapRows = fileIn.nextInt();
            mapCols = fileIn.nextInt();

            // read to the end of line
            String mapFileLine = fileIn.nextLine();

            // now we have the first line read, with rows and columns
            // need a 2-D char array to hold the map
            //char[][] mapArray = new char [mapRows][mapCols];

            // make up the row vectors row by row, when a row is complete,
            // add that to the full Vector, making a Vector of Vectors

            for ( int i = 0; i < mapRows ; ++i)
            {
                // read each subsequent line in the file
                mapFileLine = fileIn.nextLine();

                ArrayList mapRowList = new ArrayList();

                for ( int j = 0 ; j < mapCols ; ++j )
                {
                    // read each character on the line
                    mapRowList.add(mapFileLine.charAt(j));
                }

                // now put mapRowVector as an element of mapVector
                mapList.add(mapRowList); 

                System.out.println(mapList.get(i));

            }
        }
        catch ( IOException e )
        {
            System.out.println("There was an error reading the file sorry!");
        }
    }
    else
    {
        // arg length was 0 or negative
        System.out.println("Must call readMapFile with a filename as argument");
    } 
} // end readMapFile

class Terrain {

    private byte[] terrainData;
    private int terrainSizeX;
    private int terrainSizeY;

    public void init() {
        terrainData = new byte[terrainSizeX * terrainSizeY];
    }

    private int getIndex(int row, int column) {
        return terrainSizeX * column + row;
    }

    public byte getTerrainAtLocation(int row, int column) {
        return terrainData[getIndex(row, column)];
    }

    public void setTerrainAtLocation(int row, int column, byte value) {
        terrainData[getIndex(row, column)] = value;
    }
}