2D arrays

Arrays Output

100

int[][] arr = {
    {1, 2},
    {3, 4},
    {5, 6}
};

for (int[] row : arr) {
    row[0] *= 2;
}

for (int[] row : arr) {
    for (int val : row) {
        System.out.print(val + " ");
    }
}

2 2 6 4 10 6

200

What is the Outuput?

int[][] arr = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

for (int r = 0; r < arr.length; r++) {
    for (int c = 0; c < arr[r].length; c++) {
        if (r == c) {
            System.out.print(arr[r][c] + " ");
        }
    }
}

1 5 9

300

What is the output? 

int[][] arr = {
    {3, 1, 4},
    {1, 5, 9},
    {2, 6, 5}
};

for (int i = 0; i < arr.length; i++) {
    System.out.print(arr[i][i] + " ");
}

3 5 5

400

What is the output? 

int[][] arr = {
    {2, 4, 6},
    {1, 3, 5},
    {7, 8, 9}
};

int sum = 0;

for (int r = 0; r < arr.length; r++) {
    sum += arr[r][0];
}

System.out.println(sum);

10

500

The result of this:

Pokemon[] myTeam = {new Pokemon("mew", 200), new Pokemon("gible", 30)};

int[] nums = {5, 5, 5};
for(int num: nums){

      num = 10;

}
for(Pokemon mon: myTeam){

      mon.editHp(-10);

}

System.out.println(nums[0]);

System.out.println(myTeam[0].getHp());

What is:
5
190
?

2D Array

100

This expression gives the number of columns in a rectangular 2D array called arr.

What is arr[0].length?

200

What does this code output? 

int[][] arr = {
    {1, 2, 3},
    {4, 5, 6}
};

for (int[] row : arr) {
    for (int val : row) {
        val += 5;
    }
}

for (int[] row : arr) {
    for (int val : row) {
        System.out.print(val + " ");
    }
    System.out.println();
}

1 2 3

4 5 6

300

What type of loop would be best to use when summing values in each column.

Column Major 

400

This expression accesses the bottom-right element of a rectangular 2D array.

What is arr[arr.length - 1][arr[0].length - 1]?

500

The result (what nums ends up storing) of this:

int[][] nums = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
for(int i = 2; i >= 0; i--){

      for(int j = 2; j >= 0; j--){

                 if(!(i == 0 && j == 0)){

                        if(j != 0){

                             nums[i][j] += nums[i][j - 1];

                         }

                         else{

                              nums[i][j] += nums[i - 1][2];

                         }

                 }

      }

}

The result is:

[[1, 3, 5],
[7, 9, 11],
[13, 15, 17]]

More on Arrays and 2D arrays

100

This is what happens when you try to access a value at an index that doesn't exist for an array.

What is IndexOutofBounds Runtime Error?

200

Default values for values stored by int array objects if not explicitly specified

What is 0?

300

The result of:

Pokemon[] p1 = {new Pokemon("mew", 200), new Pokemon("pichu", 20)};

Pokemon[] p2 = {new Pokemon("mew", 200), new Pokemon("pichu", 20)};

System.out.println(p1 == p2);

What is false?

400

The result of:

int[] nums = {1, 2, 3};

for(int i = 0; i < 10; i--){

      System.out.println(nums[i] + 2);

}

What is error?

500

Default values for values stored by non primitive type array objects if not explicitly specified

What is null?

Key Words

100

Key words used when creating objects.

What is new?

200

Key word to indicate that a field should be shared across objects. Also indicates that a method can be called without creating an object beforehand.

What is static?

300

This Java keyword can be used on a class, method, or variable to make it accessible from any other class.

What is public?

400

This keyword is used to refer to the current object inside a class.

What is this?

500

Keyword that makes it so that you can only read from a variable once it is initially assigned a value.

What is final?