Java，正在訪問ArrayList的ArrayList的元素

Question

我確實看過訪問ArrayList <ArrayList <SomeObject >>元素，但我認為我的情況有一個更簡單的答案。 還研究了為什么Java ArrayList使用按元素進行轉換而不是按數組進行轉換？ 這似乎可以解釋潛在的演員表問題，但並不能幫助我了解此處的最佳方法。 感謝您的閱讀！

最終，我是一名Java新手，只是試圖通過將基於文本的二維地圖讀入某種數據結構來實現Map類。 由於在閱讀地圖之前我不了解地圖的大小，因此嘗試使用Vectors，但將其移至ArrayLists。

編輯這是“地圖”

12 12
MwwwppppffffMMMM
MMwwppppfffffMMM
MMMwwwwwppppffff
ffffMMMMMwwwpppp
ffffMMMMMwwwpppM
MwwwppfMMMMppfff
MwwwpffffMMMMppp
MwwwppppffffMMMM
wwppppffffMMMMMw
wppppffffMMMMMww
ppppffffMMMMMwww
pppffffMMMMMwwwp

我在類聲明下面的方法之外有這個：

// 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();

然后在我擁有的readMapFile方法中（整個方法都在最后）：

        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));

            }

然后，在嘗試訪問內部ArrayList中的元素時遇到麻煩。 這樣我得到“對象不能被轉換為ArrayList：

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

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

在嘗試運行它之前，不會給出錯誤：

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

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

我顯然需要一些幫助！ 您這里的最佳建議是什么，我只想從“地圖”中返回第x行和第y列的char。 我收到此錯誤：

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

這是我完整的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

謝謝！

Answer 1

Java的數據結構很棒，但是您必須記住基本知識:)

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;
    }
}