AP Computer Science - 2 D Arrays

//Precondition: mat is initialized

public static void matStuff(int[][] mat, int row)

{

int numCols = mat[0].length;

for (int col = 0; col < numCols; col++)

mat[row][col] = row;

}

Suppose mat is originally

1 4 9 0

2 7 8 6

5 1 4 3

After the method call matStuff(mat, 1), matrix mat will be

• 1 1 1 1

  2 7 8 6

  5 1 4 3

• 1 4 9 0

  1 7 8 6

  1 1 4 3

• 1 1 9 0

  2 1 8 6

  5 1 4 3

• 1 4 9 0

  1 1 1 1

  5 1 4 3

• 1 1 1 1

  1 1 1 1

  1 1 1 1

Which of the following initializes an 8 X 10 matrix with integer values that are prefect squares (0 is a perfect square)?

I int[][] mat = new int[8][10];

II int[][] mat = new int[8][10];

for(int r = 0; r < mat.length; r++)

for(int c = 0; c < mat[r].length; c++)

mat[r][c] = r - r;

III int[][] mat = new int[8][10];

for(int c = 0; c < mat[0].length; c++)

for(int r = 0; r < mat.length; r++)

mat[r][c] = c * c;

• I only

• II only

• III only

• I and II only

• I and III only

Given the following matrix definition:

double [][] a = new double[5][8];

This array will hold the following values after it is instantiated:

• Zeros

• False

• No values, each element will be empty

• Random Numbers

• Null

Given the following matrix definition:

boolean[][] a = new boolean[5][8];

This array will hold the following values after it is instantiated:

• Zeros

• False

• No values, each element will be empty

• Random Numbers

• Null

Consider a class that has this private instance variable:

private int[][] mat;

The class has the following method, alter.

public void alter (int c)

{

for (int i = 0; i < mat.length; i++)

for (int j = c + 1; j < mat[0].length; j++)

mat[i][j – 1] = mat [i][j];

}

If a 3 x 4 matrix mat is

1 3 5 7

2 4 6 8

3 5 7 9

then alter(1) will change mat to

• 1 5 7 7

  2 6 8 8

  3 7 9 9

• 1 5 7

  2 6 8

  3 7 9

• 1 3 5 7

  3 5 7 9

• 1 3 5 7

  3 5 7 9

  3 5 7 9

• 1 7 7 7

  2 8 8 8

  3 9 9 9

• I only

• II only

• III only

• I and II only

• I, II, and III