Unit 4c 2D-Arrays Write Code for Toggle Code

Activity 12.15.1.

Fix the errors (marked by comments) in the code so that it correctly creates a 10x10 array called table filled with numbers from 0 to 99 in left-right top-bottom order and prints the output (in row-column order) with the numbers separated by tabs. Most of the errors are syntactical, but one is logical.

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public class Test1
{
    public static void main(String[] args)
    {
        int[][] table = int[9][9]; // This line has errors
        for (int row = 0; row < table.length(); row++)  // This line has an error
        {
            for (int col = row; col < table[row].length(); col++)  // This line has errors
            {
                table[row][col] = col + 10 * row;
                System.out.print(table[row][col] + "\t");
            }
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "0   1   2   3   4   5   6   7   8   9   10  11  12  13  14  15  16  17  18  19  20"
                    + "  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36   37  38 "
                    + " 39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57 "
                    + " 58  59  60  61  62  63  64  65  66  67  68  69  70  71  72  73  74   75  76"
                    + "  77  78  79  80  81  82  83  84  85  86  87  88  89  90  91  92  93  94  95"
                    + "  96  97  98  99";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }
}

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Activity 12.15.2.

This program is supposed to create an 8x8 two-dimensional int array that is filled with a checkered patterns of 0s and 1s, starting with a 1 in the top left corner. It should also print the output in row-column order, separating each element with a space. The only missing part is the if statement that decides if a specific cell should be a 0 or a 1. Fill that in to finish the problem.

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Hint: Try drawing out a smaller version (around 4x4) of a checkered two-dimensional array. Can you notice a pattern in the row numbers and column numbers of the 1s?

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public class Test1 {
    public static void main(String[] args)
    {
        int[][] checkerboard = new int[8][8];
        for (int row = 0; row < checkerboard.length; row++)
        {
            for (int col = 0; col < checkerboard[row].length; col++)
            {
                if ()  // How can we check if a cell should be 0 or 1?
                {
                    checkerboard[row][col] = 1;
                } //end if
                System.out.print(checkerboard[row][col] + " ");
            } //end inner for loop
        } //end outer for loop
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0"
                    + " 1 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 0 1 0 1 0 1";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }
}

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Activity 12.15.3.

The sumVals method in the below program should iterate through a two-dimensional int array nums and return its sum. Fill in the headers for the for loops such that the method iterates through the entirety of nums.

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import java.util.Arrays;

public class Test1
{
    public static int sumVals(int[][] nums)
    {
        int sum = 0;

for ()   // fill in this for loop header
        {
            for ()  // fill in this for loop header
            {
                sum += nums[row][col];
            }
        }

return sum;

} //end method

public static void main(String[] args)
    {
        // You don't need to make any changes to this method
        int[][] arr1 = { {-1, 2, 0}, {6, -4, 5}, {3, 4, 8} };
        int out1 = sumVals(arr1);

System.out.println("sumVals(arr1) --> " + out1);

int[][] arr2 = { {7, -3}, {-5, 1} };
        int out2 = sumVals(arr2);

System.out.println("sumVals(arr2) --> " + out2);
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;
import java.util.Arrays;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "sumVals(arr1) --> 23\nsumVals(arr2) --> 0";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        int[][] inArr = { {2, 4, 8, 10}, {6, 0, 4, 12}};
        int expect = 46;
        int output = Test1.sumVals(inArr);

String input = stringify2DArray(inArr);
        // String output = Arrays.toString(outArr);
        // String expect = Arrays.toString(expArr);

boolean passed = getResults("" + expect, "" + output, "Running sumVals() with " + input);
        assertTrue(passed);
    }

private String stringify2DArray(int[][] mat)
    {
        String output = "[";

for (int i = 0; i < mat.length; i++)
        {
            output += Arrays.toString(mat[i]);

if (i < mat.length - 1)
            {
                 output += ", ";
            }

}

return output + "]";
    }
}

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Activity 12.15.4.

Fill in the flipImage method. This should accept a two-dimensional String array image and flip the “image” 180 degrees vertically. For example, { {"green", "red", "blue"}, {"cat", "dog", "yellow"} } would become { {"blue", "red", "green"}, {"yellow", "dog", "cat"} }.

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import java.util.Arrays;

public class Test1
{

public static void flipImage(String[][] image)
    {
        for (int row = 0; row < image.length; row++)
        {
            for (int col = 0; col < image[0].length / 2; col++)
            {
                // YOUR CODE HERE
                // Hint: this inside loop only goes until image[0].length/2 and
                // that's all you need
                // Think about swapping two elements
            } // end inner loop
        } // end outer loop
    } // end method

public static void main(String[] args)
    {
        String[][] test =
        {
            {"this", "is", "a", "test"}, {"hello", "world", "good", "luck"}
        };
        System.out.println("Before: " + Arrays.deepToString(test));
        flipImage(test);
        System.out.println("After: " + Arrays.deepToString(test));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "Before: [[this, is, a, test], [hello, world, good, luck]]\n"
                    + "After: [[test, a, is, this], [luck, good, world, hello]]";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }
}

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Activity 12.15.5.

Write the makeEvenNumbersZero method such that it iterates through the two-dimensional int array nums and replaces each instance of an even number with 0. For example, { {3, 4, 5}, {6, 7, 8} } would become { {3, 0, 5}, {0, 7, 0} }.

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Activity 12.15.6.

Fill in the numOccurrences method. It should take in a two-dimension int array nums and an int desired and return the number of times that desired appears in nums. E.g., with { {3, 1, 2}, {3, 4, 1} } as nums, numOccurrences(nums, 1) should return 2.

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Activity 12.15.7.

Fill in the averageCols method. It should accept a two-dimensional int array nums and return a one-dimensional (normal) int array containing the integer average of each of the columns (NOT the rows). E.g., with nums as { {3, 5, 2}, {1, 1, 6} }, averageCols(nums) should return {2, 3, 4} as that is (3 + 1) / 2, (5 + 1) / 2, and (2 + 6) / 2.

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Activity 12.15.8.

Write the oddRows method. This should take in a two-dimensional int array nums and return a new two-dimensional int array containing only the odd-index rows. For example, with nums equal to { {3, 2, 1}, {4, 5, 6}, {1, 5, 7} }, oddRows(nums) would return { {4, 5, 6} } as that was the row at index 1, which is the only odd index present.

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import java.util.Arrays;

public class Test1
{

public static int[][] oddRows(int[][] nums)
    {

int[][] odds = new int[nums.length / 2][nums[0].length];

// YOUR CODE HERE

return odds;
    } // end method

public static void main(String[] args)
    {
        int[][] arr1 = { {-1, 2, 0}, {6, -4, 5}, {3, 4, 8}};
        int[][] out1 = oddRows(arr1);

// Arrays.deepToString is a method that prints 2d arrays nicely
        System.out.println("oddRows(arr1) --> " + Arrays.deepToString(out1));

int[][] arr2 = { {7, -3}, {-5, 1}, {2, 4}, {8, 5}};
        int[][] out2 = oddRows(arr2);

System.out.println("oddRows(arr2) --> " + Arrays.deepToString(out2));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;
import java.util.Arrays;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "oddRows(arr1) --> [[6, -4, 5]]\noddRows(arr2) --> [[-5, 1], [8, 5]]";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        int[][] inArr = { {2, 4, 8, 10}, {6, 0, 4, 12}, {1, 3, 5, 7}, {8, 6, 4, 2}};
        String expect = "[[6, 0, 4, 12], [8, 6, 4, 2]]";
        String output = Arrays.deepToString(Test1.oddRows(inArr));

String input = Arrays.deepToString(inArr);
        // String output = Arrays.toString(outArr);
        // String expect = Arrays.toString(expArr);

boolean passed = getResults(expect, output, "Running oddRows() with " + input);
        assertTrue(passed);
    }
}

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Activity 12.15.9.

Write the breakIntoLetters method. It should accept a two-dimensional String array, in which each row contains the characters of a word. It should then return a single-dimensional (normal) String array containing the words in each row of the two-dimensional array. For example, calling breakIntoLetters on { {“b”, “a”, “t”, “h”}, {“t”, “e”, “n”, “s”}, {“j”, “a”, “c”, “k”}, {“l”, “a”, “z”, “y”} } should return {“bath”, “tens”, “jack”, “lazy”}.

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import java.util.Arrays;

public class Test1
{

public static String[] breakIntoLetters(String[][] words)
    {

// YOUR CODE HERE

} // end method

public static void main(String[] args)
    {
        String[][] mat1 =
        {
            {"b", "a", "t", "h"},
            {"t", "e", "n", "s"},
            {"j", "a", "c", "k"},
            {"l", "a", "z", "y"}
        };
        String[] out1 = breakIntoLetters(mat1);

System.out.println("mat1 --> " + Arrays.deepToString(mat1));
        System.out.println("breakIntoLetters(mat1) --> " + Arrays.toString(out1));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;
import java.util.Arrays;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "mat1 --> [[b, a, t, h], [t, e, n, s], [j, a, c, k], [l, a, z, y]]\n"
                    + "breakIntoLetters(mat1) --> [bath, tens, jack, lazy]";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        String[][] inArr =
        {
            "computer".split(""), "science".split(""), "rocks".split(""),
        };
        String expect = "[computer, science, rocks]";
        String output = Arrays.toString(Test1.breakIntoLetters(inArr));

String input = Arrays.deepToString(inArr);
        // String output = Arrays.toString(outArr);
        // String expect = Arrays.toString(expArr);

boolean passed = getResults(expect, output, "Running breakIntoLetters() with " + input);
        assertTrue(passed); /**/
    }
}

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Activity 12.15.10.

Write the maxEachRow method. It that should accept a two-dimensional int array nums, and return a single-dimensional (normal) int array containing the max of each row. For example, the returned array for { {3}, {4, 9, 6, -1}, {45, 1} } should be {3, 9, 45}.

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import java.util.Arrays;

public class Test1
{

public static int[] maxEachRow(int[][] nums)
    {

// YOUR CODE HERE

} // end method

public static void main(String[] args)
    {
        int[][] mat1 = { {-1, 2, 0}, {6, -4, 5}, {3, 4, 8}};
        int[] out1 = maxEachRow(mat1);

System.out.println("mat1 --> " + Arrays.deepToString(mat1));
        System.out.println("maxEachRow(mat1) --> " + Arrays.toString(out1));

int[][] mat2 = { {7, -3}, {-5, 1}};
        int[] out2 = maxEachRow(mat2);

System.out.println("mat2 --> " + Arrays.deepToString(mat2));
        System.out.println("maxEachRow(mat2) --> " + Arrays.toString(out2));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;
import java.util.Arrays;

public class RunestoneTests extends CodeTestHelper
{
    public RunestoneTests()
    {
        super("Test1");
    }

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "mat1 --> [[-1, 2, 0], [6, -4, 5], [3, 4, 8]]\n"
                    + "maxEachRow(mat1) --> [2, 6, 8]\n"
                    + "mat2 --> [[7, -3], [-5, 1]]\n"
                    + "maxEachRow(mat2) --> [7, 1]";

boolean passed = getResults(expect, output, "Running main");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        int[][] inArr = { {2, 4, 8, 10}, {6, 0, 4, 12}};
        String expect = "[10, 12]";
        String output = Arrays.toString(Test1.maxEachRow(inArr));

String input = Arrays.deepToString(inArr);
        // String output = Arrays.toString(outArr);
        // String expect = Arrays.toString(expArr);

boolean passed = getResults(expect, output, "Running maxEachRow() with " + input);
        assertTrue(passed);
    }
}

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CSAwesome2 AP CSA Java 2025+

Section 12.15 Unit 4c 2D-Arrays Write Code for Toggle Code

Activity 12.15.1.

Activity 12.15.2.

Activity 12.15.3.

Activity 12.15.4.

Activity 12.15.5.

Activity 12.15.6.

Activity 12.15.7.

Activity 12.15.8.

Activity 12.15.9.

Activity 12.15.10.