9.5. Code Practice with 2D Arrays

Replace the “ADD CODE HERE” below with the code to declare and create a 3 by 3 two-dimensional int array named table. The finished code will print the values 0 to 8.

public class Test1 { public static void main(String[] args) { // ADD CODE HERE // // Should print the values in table int count = 0; for (int row = 0; row < table.length; row++) { for (int col = 0; col < table.length; col++) { table[row][col] = count; count++; System.out.print(table[row][col] + " "); } } } }

Declaring and creating a 3 by 3 two-dimensional int array only takes one line. To declare the array specify the type of values in the array followed by [][] to indicate a 2D array and then provide a name for the array. To create the array add an = new, followed by the same type as before and [num rows][num cols].

public class Test1 { public static void main(String[] args) { int[][] table = new int[3][3]; int count = 0; for (int row = 0; row < table.length; row++) { for (int col = 0; col < table[0].length; col++) { table[row][col] = count; count++; System.out.print(table[row][col] + " "); } } } }

Replace the “ADD CODE HERE” below with the code to declare and initialize a two-dimensional String array called students with the names “Brice, Marvin, Anna” in the first row and “Kamal, Maria, Elissa” in the second. The finished code will print all the names in the array starting with all in the first row followed by all in the second row.

public class Test1 { public static void main(String[] args) { // ADD CODE HERE // // Should print the values in students in order for (int row = 0; row < students.length; row++) { for (int col = 0; col < students[0].length; col++) { System.out.print(students[row][col] + " "); } } } }

Print the values 47, 51, and 20 by accessing them in the the given two-dimensional array.

public class Test1 { public static void main(String[] args) { int[][] arr = { {47,3,12},{51,74,20} }; // ADD CODE HERE // } }

Print the values 8, 3, 87, and 34 by accessing them from the given two-dimensional array.

public class Test1 { public static void main(String[] args) { int[][] arr = { {10,39,8},{3},{35,87},{22},{34} }; // ADD CODE HERE // } }

Print the number of rows in the given two-dimensional array, or the length of the outer array. Then print the number of columns, or the length of each inner array.

Ex. The array { {“hello”,”there”,”world”},{“how”,”are”,”you”} } should print:

Rows: 2

Columns: 3

public class Test1 { public static void main(String[] args) { String[][] arr = { {"hello","there","world"}, {"how","are","you"} }; System.out.println("Rows:"); // ADD CODE TO PRINT NUMBER OF ROWS HERE // System.out.println("Columns:"); // ADD CODE TO PRINT NUMBER OF COLUMNS HERE // } }

Loop through the given two-dimensional array, printing out the values in the first row followed by those in the second row and so on.

public class Test1 { public static void main(String[] args) { String[][] arr = { {"Hey ", "there! "},{"I ", "hope "}, {"you ", "are "}, {"doing ", "well"} }; // ADD CODE HERE // } }

Declare and create a two-dimensional array of strings named colors. Put the colors (“red”, “yellow”, “blue”) in the first row, and the colors (“orange”, “green”, “purple”) in the second row. Then print every value in the array.

public class Test1 { public static void main(String[] args) { // ADD CODE HERE // } }

Replace the “ADD CODE HERE” below with the code to count and print the number of 7’s that are in the 2d array. It should print 2.

public class Test1 { public static void main(String[] args) { int[][] array = { {4,7,8},{8,8,7} }; //ADD CODE HERE } }

Replace the “ADD CODE HERE” below with the code to print out the sum of the numbers in the second row of the “table” array. It should print 18.

public class Test1 { public static void main(String[] args) { int[][] table = { {1,4,9},{11,4,3},{2,2,3} }; //ADD CODE HERE } }

Replace the “ADD CODE HERE” below with the code to find the sum of the values on the diagonal from [0][0] to [num rows - 1][num rows - 1] Print the sum. It should print 5.

public class Test1 { public static void main(String[] args) { int[][] array = { {1,2,3},{-1,-2,-3},{4,5,6} }; //ADD CODE HERE } }

Replace the “ADD CODE HERE” below with the code to declare and create a two-dimensional array of integers numbers with the numbers (1,2,3) in the first row, and the numbers (4,5,6) in the second row. Then loop through the two-dimensional array, printing out the values in the first row followed by those in the second row.

public class Test1 { public static void main(String[] args) { // ADD CODE HERE // } }

Replace the “ADD CODE HERE” below with the code to declare and create a two-dimensional array of integers numbers with the numbers (1,2,3) in the first row, the numbers (4,5,6) in the second row, and the numbers (7,8,9) in the third row. Then loop through the two-dimensional array, printing out the values in the first row followed by those in the second row and so on.

public class Test1 { public static void main(String[] args) { // ADD CODE HERE // } }

Given the following array, replace the “ADD CODE HERE” below with the code to replace the word “purple” with “yellow”.

public class Test1 { public static void main(String[] args) { String[][] arr = { {"red","orange", "purple"}, {"green","blue", "indigo"} }; // ADD CODE HERE // for (int row = 0; row < arr.length; row++) { for (int col = 0; col < arr[1].length; col++) { System.out.println(arr[row][col]); } } } }

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