使用嵌套循环创建二维数组

Question

I am trying to understand this code from the book.

int[][] grade = {
  { 1, 0, 1 },
  { 0, 1, 0 },
  { 1, 0, 1 }
};
for (int i = 0; i < 3; i++) {
  for (int j = 0; j < 3; j++) {
    if (i == j)
      System.out.print(grade[i][j] + grade[j][i] + " ");
    else
      System.out.print(grade[i][j] * grade[j][i] + " ");
  }
  System.out.println(" ");
}

I understand the logic of a two-dimensional arrays being rows and columns. I just don't understand how the answer came to be this.

2 0 1
0 2 0
1 0 2

Answer 1

It loops through the 2 dimensional array. If i is equal to j, eg ( 0,0 1,1 2,2 ) then it adds grade[i][j] with grade[j][i]. Since i and j are equal it adds the location with itself.

When i is not equal to j it multiplies grade[i][j] with grade[j][i].

Since they are not equal it multiplies 2 different positions in the grid. eg

grade [3][1] is multiplied by grade[1][3], not by itself.

If you changed grade[1][3] to 2, then all corners would be output as 2

The input:

1 0 2
0 1 0
1 0 1

would output:

2 0 2
0 2 0
2 0 2

Answer 2

It basically loops through the two dimensional array and if it sees that the column and row number (i and j) are the same it will add it with itself. ie times the diagonal by two. And for the rest of the entries it will multiply with itself.