Consider the following code segment.

int[][] mat = new int[5][3];
for (int j = 0; j

Question

Consider the following code segment.

int[][] mat = new int[5][3];
for (int j = 0; j < mat.length; j++) 
{
  for (int k = 0; k < mat[0].length; k++) 
  {
    mat[j][k] = 10 * k + j;
  }
}

What are the contents of mat after the code segment has been executed?

BlackTom AI · Accepted Answer

A 5×3 int matrix mat is created and filled by nested loops. In Java, mat.length is the number of rows (5) and mat[0].length is the number of columns (3). The outer loop variable j indexes rows (0..4) and the inner loop variable k indexes columns (0..2). Each entry is assigned mat[j][k] = 10 * k + j, so the column index k is multiplied by 10 and the row index j is added.

Step-by-step evaluation (showing each assignment):
- For j = 0:
  - k = 0: mat[0][0] = 10*0 + 0 = 0
  - k = 1: mat[0][1] = 10*1 + 0 = 10
  - k = 2: mat[0][2] = 10*2 + 0 = 20
  Row 0 => {0, 10, 20}

- For j = 1:
  - k = 0: mat[1][0] = 10*0 + 1 = 1
  - k = 1: mat[1][1] = 10*1 + 1 = 11
  - k = 2: mat[1][2] = 10*2 + 1 = 21
  Row 1 => {1, 11, 21}

- For j = 2:
  - k = 0: mat[2][0] = 10*0 + 2 = 2
  - k = 1: mat[2][1] = 10*1 + 2 = 12
  - k = 2: mat[2][2] = 10*2 + 2 = 22
  Row 2 => {2, 12, 22}

- For j = 3:
  - k = 0: mat[3][0] = 3
  - k = 1: mat[3][1] = 13
  - k = 2: mat[3][2] = 23
  Row 3 => {3, 13, 23}

- For j = 4:
  - k = 0: mat[4][0] = 4
  - k = 1: mat[4][1] = 14
  - k = 2: mat[4][2] = 24
  Row 4 => {4, 14, 24}

Putting all rows together produces:
{{0, 10, 20},
 {1, 11, 21},
 {2, 12, 22},
 {3, 13, 23},
 {4, 14, 24}}

Why this is correct: the formula uses k as the tens place (10*k) and adds the row index j, so values vary slowly down rows (j increments by 1) and jump by 10 across columns (k increments by 1). Common incorrect answers would transpose rows and columns (e.g., {0,1,2},{10,11,12},...) which would result if someone mistakenly treated k as the row index or swapped indices; that does not match the assignment mat[j][k] = 10*k + j used here.

Final confirmation: the contents of mat are exactly {{0, 10, 20}, {1, 11, 21}, {2, 12, 22}, {3, 13, 23}, {4, 14, 24}}, matching the provided answer.

Consider the following code segment. int[][] mat = new int[5][3]; for (int j = 0; j < mat.length; j++) { for (int k = 0; k < mat[0].length; k++) { mat[j][k] = 10 * k + j; } } What are the contents of mat after the code segment has been executed?单项选择题

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