ArrayList中的数组问题，Java

Question

我创建了一个名为current_map的多维数组

我正在尝试访问current_map：

current_map[0][1]

但是，我收到了错误：

error: array required, but String found

这是我的代码，供您观赏

import java.util.*;
import java.util.Map.Entry;
import java.util.ArrayList;
public class TestApp {
    private ArrayList<String[]> current_map = new ArrayList<String[]>();
    public TestApp() {
        current_map.add(new String[] { "0","0","0" });
        current_map.add(new String[] { "0","Q","0" });
        current_map.add(new String[] { "0","0","0" });
    }
    public String getValue(int X,int Y){
        String[] obj_map = current_map.toArray(new String[current_map.size()]);
        return obj_map[X][Y]; // for example, getValue(2,2), should give "Q"
    }
}

我怎样才能阻止这个问题

Answer 1

您可以这样做：

import java.util.*;
import java.util.Map.Entry;
import java.util.ArrayList;
public class TestApp {
    private ArrayList<String[]> current_map = new ArrayList<String[]>();
    public TestApp() {
        current_map.add(new String[] { "0","0","0" });
        current_map.add(new String[] { "0","Q","0" });
        current_map.add(new String[] { "0","0","0" });
    }
    public String getValue(int X,int Y){
        return current_map.get(Y)[X]; // for example, getValue(2,2), should give "Q"
    }

    public static void main(String[] args) {
      TestApp ta = new TestApp();
      System.out.println(ta.getValue(1, 1));
    }

}

注意，在Java数组中，索引是基于0的，所以第二行第二列用（1，1）表示，而不是（2，2）

希望这有帮助

Answer 2

除非有令人信服的理由对每个get命令进行完整复制，否则应该使用现有结构

public String getValue(int X, int Y)
{
  return current_map.get(X)[Y];
}

Answer 3

您所拥有的并不是真正的多维表示，因为您访问不同维度的方式并不一致。它的语义，但要称之为真正的多维（包括符号），您需要这样的东西（请参考this了解此代码的源代码。我不是此代码的所有者。）

import java.util.ArrayList;

public class ArrayList2d<Type>
{
    ArrayList<ArrayList<Type>>  array;

    public ArrayList2d()
    {
        array = new ArrayList<ArrayList<Type>>();
    }

    /**
     * ensures a minimum capacity of num rows. Note that this does not guarantee
     * that there are that many rows.
     * 
     * @param num
     */
    public void ensureCapacity(int num)
    {
        array.ensureCapacity(num);
    }

    /**
     * Ensures that the given row has at least the given capacity. Note that
     * this method will also ensure that getNumRows() >= row
     * 
     * @param row
     * @param num
     */
    public void ensureCapacity(int row, int num)
    {
        ensureCapacity(row);
        while (row < getNumRows())
        {
            array.add(new ArrayList<Type>());
        }
        array.get(row).ensureCapacity(num);
    }

    /**
     * Adds an item at the end of the specified row. This will guarantee that at least row rows exist.
     */
    public void add(Type data, int row)
    {
        ensureCapacity(row);
        while(row >= getNumRows())
        {
            array.add(new ArrayList<Type>());
        }
        array.get(row).add(data);
    }

    public Type get(int row, int col)
    {
        return array.get(row).get(col);
    }

    public void set(int row, int col, Type data)
    {
        array.get(row).set(col,data);
    }

    public void remove(int row, int col)
    {
        array.get(row).remove(col);
    }

    public boolean contains(Type data)
    {
        for (int i = 0; i < array.size(); i++)
        {
            if (array.get(i).contains(data))
            {
                return true;
            }
        }
        return false;
    }

    public int getNumRows()
    {
        return array.size();
    }

    public int getNumCols(int row)
    {
        return array.get(row).size();
    }
}

Answer 4

您已经说过obj_map是一个String[]，但在下一行中，您将其视为一个2D数组