二维数组| 爪哇

Question

I have code which creates a two dimensional array but I want to modify this code so that instead of int, class Integer is used; and instead of arrays, nested ArrayList is used.

How do I achieve this? Thank you.

public class Array {
   int[][] fillMatrix() {
      int[][] matrix = new int[5][4];
      for (int row = 0; row < 5; row++) {
          for (int column = 0; column < 4; column++) {
              matrix[row][column] = row * column;
          }
      }
      return matrix;
   }
}

Answer 1

All you need is a

List<List<Integer>> matrix;

This is a list of a list. so the 0 position will hold the column / row based on the implementation.

Your code should look like

List<List<Integer>> matrix = new ArrayList<List<Integer>>;
    for (int row = 0; row < 5; row++) {
        matrix.add(new ArrayList<Integer>())
        for (int column = 0; column < 4; column++) {
             matrix.get(row).add(row * column);
        }
    }
    return matrix;
}

PS code not tested may need small tweaks but it should provide a good guideline.

Answer 2

import java.util.ArrayList;
import java.util.List;

public class Array {
    List<ArrayList<Integer>> matrix = new ArrayList<ArrayList<Integer>>();

    List<ArrayList<Integer>> fillMatrix() {
        for (int row = 0; row < 5; row++) {
            matrix.add(new ArrayList<Integer>());
            for (int column = 0; column < 4; column++) {
                matrix.get(row).add(column,  row * column);
            }
        }
        return matrix;
    }
}