Issues with an Array in an ArrayList, Java

Question

I created a multidimensional array called current_map.

I am trying to access current_map:

current_map[0][1]

However I receive the error:

error: array required, but String found

Here is my code for your viewing pleasure

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"
    }
}

How can I stop this issue?

icyrock.com · Accepted Answer · 2012-03-27 02:57:52Z

6

You can do something like this:

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));
    }

}

Note that in Java array indexes are 0-based, so 2nd row, 2nd column is represented with (1, 1), not (2, 2).

Hope this helps.

answered Mar 27, 2012 at 2:57

icyrock.com

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Comments

Thomas · Accepted Answer · 2012-03-27 02:58:07Z

2

Unless there's compelling reason to do a full copy on every get command, you should use your existing structure.

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

answered Mar 27, 2012 at 2:58

Thomas

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Comments

John3136 · Accepted Answer · 2012-03-27 02:59:36Z

2

You have said obj_map is a String[], but in the very next line you treat it as a 2D array.

answered Mar 27, 2012 at 2:59

John3136

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Comments

uaarkoti · Accepted Answer · 2012-03-27 03:04:44Z

What you have is not really a true multi-dimension representation as the way you access different dimensions is not consistent. Its semantics but to call it a true multi-dimensional (including symantics) you need something like this (Please refer this for the source of this code. I am not the owner of this code.)

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();
    }
}

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