Unit 4b ArrayList Write Code for Toggle Code

Activity 12.14.1.

The following program should create an ArrayList called conversation, add in some elements("hello", "goodbye", "how are you", and "see you later"), and print out the elements with ", " after each. Fill in the code so that it adds the elements to conversation. The rest of the program is finished for you.

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import java.util.ArrayList;
import java.util.List;

public class ListTest
{

public static void main(String[] args)
    {

ArrayList<String> conversation;
        conversation = new ArrayList<String>();

// YOUR CODE HERE //

for (String element : conversation)
        {

System.out.print(element + ", ");
        }
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "hello, goodbye, how are you, see you later,";

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

// @Test
    public void test2()
    {
        String code = getCodeWithoutComments();
        System.out.println("Stuck here");

int count = countOccurences(code, "new ArrayList");
        boolean passed = getResults("1", "" + count, "Counting number of new ArrayList");
        assertTrue(passed);
    }

// @Test
    public void test3()
    {
        String code = getCodeWithoutComments();
        // System.out.println("Stuck here");
        int count = countOccurences(code, ".add(");
        boolean passed = getResults("4", "" + count, "Counting number of .add()");
        assertTrue(passed);
    }
}

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Activity 12.14.2.

Fix the two errors in the printBackwards method so that it will correctly iterate through the parameter myList backwards and print each element.

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import java.util.ArrayList;

public class ListTest
{

public static void printBackwards(ArrayList<String> myList)
    {

for (int i = myList.size() - 1; i > 0; i--)
        {

System.out.print(myList[i] + ", ");
        }
    }

public static void main(String[] args)
    {

ArrayList<String> conversation;
        conversation = new ArrayList<String>();

conversation.add("hello");
        conversation.add("goodbye");
        conversation.add("how are you");
        conversation.add("see you later");

printBackwards(conversation);
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

// import java.util.ArrayList;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "see you later, how are you, goodbye, hello,";

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

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Activity 12.14.3.

Write code to define the removeZeros method. This method should take in an ArrayList of integers listOfNums and delete all of the zeros. For example, {3, 0, 5, 0} would change into {3, 5}.

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import java.util.ArrayList;

public class ListTest
{

public static void removeZeros(ArrayList<Integer> listOfNums)
    {
        // YOUR CODE HERE

// HINT: When you delete an element, the indexes of the following elements
        // shift!
        // That means you CANNOT use an enhanced for loop
        // And it also means you need to carefully handle when you increment your
        // index variable

}

public static void main(String[] args)
    {

ArrayList<Integer> list;
        list = new ArrayList<Integer>();

list.add(1);
        list.add(0);
        list.add(0);
        list.add(3);
        list.add(2);
        list.add(0);
        list.add(9);

System.out.println("Before: " + list);
        removeZeros(list);
        System.out.println("After: " + list);
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

// import java.util.ArrayList;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "Before: [1, 0, 0, 3, 2, 0, 9]\nAfter: [1, 3, 2, 9]";

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

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Activity 12.14.4.

Write code for the findSmallest method. This code segment should take in an ArrayList nums and return the smallest element present. For example, findSmallest called on {5, 3, 1, 6} should return 1.

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Activity 12.14.5.

Write code to flesh out the removeOdd method. This method should take in a parameter nums and delete every odd number from it. For example, {5, 3, 2, 1, 4} should become {2, 4}.

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import java.util.ArrayList;

public class ListTest
{

public static void removeOdd(ArrayList<Integer> nums)
    {

// YOUR CODE HERE //
        // Just like in problem three, be wary about the changing indexes

}

public static void main(String[] args)
    {

ArrayList<Integer> list;
        list = new ArrayList<Integer>();

list.add(12);
        list.add(7);
        list.add(16);
        list.add(39);
        list.add(28);
        list.add(40);
        list.add(9);

System.out.println("Before: " + list);
        removeOdd(list);
        System.out.println("After: " + list);
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "[12, 16, 28, 40]";

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

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Activity 12.14.6.

Fill out the average method. It should take in an ArrayList nums and calculate the arithmetic mean (the sum divided by the length). For example, average called on {5, 9, 6} should return 6.66666666667 as that is (5 + 9 + 6) / 3.

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Activity 12.14.7.

Create the moveLargest method. This should find the largest value in an ArrayList of Integers (the parameter) and move it to the back of the list.

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import java.util.ArrayList;

public class ListTest
{

public static void moveLargest(ArrayList<Integer> nums)
    {

// YOUR CODE HERE //

} // end moveLargest method

public static void main(String[] args)
    {

ArrayList<Integer> list;
        list = new ArrayList<Integer>();

list.add(1);
        list.add(3);
        list.add(12);
        list.add(0);
        list.add(9);

System.out.println("Before: " + list);
        moveLargest(list);
        System.out.println("After: " + list);
    } // end main method
} // end class
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

// import java.util.ArrayList;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "Before: [1, 3, 12, 0, 9]\nAfter: [1, 3, 0, 9, 12]";

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

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Activity 12.14.8.

Write code to finish the removeShort method. It should take an ArrayList words and remove all elements that are three characters long or shorter. For example, {"Dog", "Monkey", "Lion", "Cat"} would become {"Monkey", "Lion"}.

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import java.util.ArrayList;

public class ListTest
{

public static void removeShort(ArrayList<String> words)
    {

// YOUR CODE HERE //
        // Just like in problem three, consider iterating backwards or using a
        // while loop

} // end removeShort method

public static void main(String[] args)
    {

ArrayList<String> list;
        list = new ArrayList<String>();

list.add("catch");
        list.add("dog");
        list.add("tree");
        list.add("me");

System.out.println("Before: " + list);
        removeShort(list);
        System.out.println("After: " + list);
    } // end main method
} // end class
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "Before: [catch, dog, tree, me]\nAfter: [catch, tree]";

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

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Activity 12.14.9.

Write the method doubleList. This should take in an ArrayList words and insert a copy of each element such that {"cat", "ribbon", "house"} would become {"cat", "cat", "ribbon", "ribbon", "house", "house"}.

🔗

import java.util.ArrayList;

public class ListTest
{

public static void doubleList(ArrayList<String> words)
    {

// YOUR CODE HERE
        // Remember - when you insert elements, you'll change the indexes!

} // end doubleList method

public static void main(String[] args)
    {

ArrayList<String> list;
        list = new ArrayList<String>();

list.add("catch");
        list.add("dog");
        list.add("tree");
        list.add("me");

System.out.println("Before: " + list);
        doubleList(list);
        System.out.println("After: " + list);
    } // end main method
} // end class
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect =
                "Before: [catch, dog, tree, me]\n"
                    + "After: [catch, catch, dog, dog, tree, tree, me, me]";

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

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Activity 12.14.10.

Write the method removeElement. This should take in an ArrayList nums and an integer toRemove and remove every instance of that integer from nums. E.g., if nums was {3, 6, 5, 3, 4}, it should become {6, 5, 4} after calling removeElement(nums, 3).

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import java.util.ArrayList;

public class ListTest
{

public static void removeElement(ArrayList<Integer> nums, int toRemove)
    {

// YOUR CODE HERE

} // end average method

public static void main(String[] args)
    {

ArrayList<Integer> list;
        list = new ArrayList<Integer>();

list.add(1);
        list.add(3);
        list.add(2);
        list.add(9);

System.out.println("Before: " + list);
        removeElement(list, 3);
        System.out.println("After: " + list);
    } // end main method
} // end class
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;

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

@Test
    public void test1()
    {
        String output = getMethodOutput("main");
        String expect = "Before: [1, 3, 2, 9]\nAfter: [1, 2, 9]";

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

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CSAwesome2 AP CSA Java 2025+

Section 12.14 Unit 4b ArrayList Write Code for Toggle Code

Activity 12.14.1.

Activity 12.14.2.

Activity 12.14.3.

Activity 12.14.4.

Activity 12.14.5.

Activity 12.14.6.

Activity 12.14.7.

Activity 12.14.8.

Activity 12.14.9.

Activity 12.14.10.