Code Practice with 2D Arrays

Activity 4.48.1.

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] + " ");
            }
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "0 1 2 3 4 5 6 7 8";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testContains()
    {
        String target = "int[][] table = new int[3][3];";
        boolean passed = checkCodeContains("3x3 declaration of int array table", target);
        assertTrue(passed);
    }
}

Activity 4.48.2.

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] + " ");
            }
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "Brice Marvin Anna Kamal Maria Elissa";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testContains()
    {
        String target = "String[][] students";
        boolean passed = checkCodeContains("2D String array called students", target);
        assertTrue(passed);
    }
}

Activity 4.48.3.

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

Activity 4.48.4.

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 //

}
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testOutput() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "8\n3\n87\n34";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void testDigitOne() throws IOException
    {
        String target = "arr[0][2]";
        boolean passed = checkCodeContains("Correct accessing of 8", target);
        assertTrue(passed);
    }

@Test
    public void testDigitTwo() throws IOException
    {
        String target = "arr[1][0]";
        boolean passed = checkCodeContains("Correct accessing of 3", target);
        assertTrue(passed);
    }

@Test
    public void testDigitThree() throws IOException
    {
        String target = "arr[2][1]";
        boolean passed = checkCodeContains("Correct accessing of 87", target);
        assertTrue(passed);
    }

@Test
    public void testDigitFour() throws IOException
    {
        String target = "arr[4][0]";
        boolean passed = checkCodeContains("Correct accessing of 34", target);
        assertTrue(passed);
    }
}

Activity 4.48.5.

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.

public class Test1
{

public static void main(String[] args)
    {
        String[][] arr = { {"hello", "there", "world"}, {"how", "are", "you"}};

System.out.print("Rows:");
        // ADD CODE TO PRINT NUMBER OF ROWS HERE using arr //

System.out.print("Columns:");
        // ADD CODE TO PRINT NUMBER OF COLUMNS HERE using arr //

}
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "Rows:2\nColumns:3";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        String target = "arr.length";
        boolean passed = checkCodeContains("using arr and length to get number of rows", target);
        assertTrue(passed);
    }

@Test
    public void test3()
    {
        String target = "arr[0].length";
        boolean passed =
                checkCodeContains("using arr[0] and length to get number of columns", target);
        assertTrue(passed);
    }
}

Activity 4.48.6.

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 //

}
}
====

import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
      {
          @Test
          public void testMain() throws IOException
          {
              String output = getMethodOutput("main");
              String expect = "Hey there! \nI hope \nyou are \ndoing well ";
              boolean passed = getResults(expect, output, "Expected output from main");
              assertTrue(passed);
          }

@Test
          public void test1()
          {
              String code = getCode();
              String target = "for";

int num = countOccurences(code, target);
              boolean passed = (num >= 2);

getResults("2", "" + num, "2 for loops", passed);
              assertTrue(passed);
          }
      }

Activity 4.48.7.

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 //
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testArrayDec() throws IOException
    {
        String code = removeSpaces(getCode());
        String expect =
                removeSpaces(
                        "String[][] colors = { {\"red\", \"yellow\", \"blue\"},{\"orange\","
                            + " \"green\", \"purple\"}}");

boolean passed = code.contains(expect);
        getResults("true", passed + "", "correct initialization of array", passed);
        assertTrue(passed);
    }

@Test
    public void testOutput() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "red yellow blue \norange green purple";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }
}

Activity 4.48.8.

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

}
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "2";
        boolean passed = output.contains(expect);
        getResults(expect, output, "Expected output from main", passed);
        assertTrue(passed);
    }

@Test
    public void test1()
    {
        String target = "for";
        int num = countOccurences(getCode(), target);
        boolean passed = (num == 2);
        getResults("2", num + "", "2 for loops", passed);
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        String target = "if (array[*][*] == 7)";
        boolean passed =
                checkCodeContains("if statement checking if array[*][*] element equals 7", target);
        assertTrue(passed);
    }
}

Activity 4.48.9.

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.

Activity 4.48.10.

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.

Activity 4.48.11.

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.

Activity 4.48.12.

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 //
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "1 2 3\n4 5 6\n7 8 9";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void test1()
    {
        String expect = "int[][] numbers = { {1,2,3},{4,5,6}, {7,8,9}}";
        boolean passed = checkCodeContains("correct array initialization", expect);
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        String target = "for";
        int num = countOccurences(getCode(), target);
        boolean passed = (num == 2);
        getResults("2", num + "", "2 for loops", passed);
        assertTrue(passed);
    }
}

Activity 4.48.13.

Given the following array, replace the “ADD CODE HERE” below with 1 line of code to replace the word “purple” with “yellow” using the correct array location.

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]);
            }
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    @Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect = "red\norange\nyellow\ngreen\nblue\nindigo\n";
        boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void test1() throws IOException
    {
        String expect = "arr[0][2] = \"yellow\"";
        boolean passed = checkCodeContains("replacing correct array element with yellow", expect);
        assertTrue(passed);
    }
}

Section 4.48 Code Practice with 2D Arrays

Activity 4.48.1.

Activity 4.48.2.

Activity 4.48.3.

Activity 4.48.4.

Activity 4.48.5.

Activity 4.48.6.

Activity 4.48.7.

Activity 4.48.8.

Activity 4.48.9.

Activity 4.48.10.

Activity 4.48.11.

Activity 4.48.12.

Activity 4.48.13.