Unit 7: ArrayList

Mastering the concept of Java’s ArrayList. AP Exam weighting: 2.5-7.5%.

7.1: ArrayList Intro

ArrayLists are dynamic, meaning their size can grow or shrink as needed, but arrays are static in size
Instead of creating a new array of a different size and copying the data from the initial array to the new one, we can use ArrayLists

Arrays	ArrayLists
Fixed Length	Resizable Length
Fundamental Java feature	Part of a framework
An object with no methods	Class with many methods
Not as flexible	Designed to be very flexible
Can store primitive data	Not designed to store primitives
	Slightly slower than arrays
	Need an import statement

In order to use the ArrayList class, the ArrayList class needs to be imported from the java util package. This can be done by writing import java.util.ArrayList at the top of the class file.

import java.util.ArrayList;  // Import the ArrayList class

// Declare and initialize an ArrayList of integers
ArrayList<Integer> numbersList = new ArrayList<>();

ArrayList objects are created in the same fashion as other object classes. The primary difference with ArrayLists is that the element type of the ArrayList must be specified using angled bracket <>. In this example, E represents the data type that will be used in the ArrayList. This can be replaced by an object data type:

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

We can actually declare ArrayLists without specifying the type that will be included in the ArrayList, but specifying the data type is smarter because it allows the compiler to find errors before run time, so its more efficient and easy to spot errors.

ArrayList list = new ArrayList();

Quick lil popcorn hack

Create 2 ArrayLists, 1 called studentName and 1 called studentAge

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        // Create an ArrayList for student names
        ArrayList<String> studentName = new ArrayList<String>();

        // Create an ArrayList for student ages
        ArrayList<Integer> studentAge = new ArrayList<Integer>();
    }
}

7.2: ArrayList Methods

Learning Objectives

Students will be able to represent collections of related object reference data using ArrayList objects.

Essential Knowledge

Iteration statements provide a means to access all the elements stored within an ArrayList. This process is referred to as “traversing the ArrayList.”
The following ArrayList methods, including what they do and when they are used, are part of the Java Quick Reference:
- int size() - Returns the count of elements within the list.
- boolean add(E obj) - Appends the object obj to the end of the list and returns true.
- void add(int index, E obj) - Inserts obj at the specified index, shifting elements at and above that position to the right (incrementing their indices by 1) and increasing the list’s size by 1.
- E get(int index) - Retrieves the element at the given index in the list.
- E set(int index, E obj) - Replaces the element at the specified index with obj and returns the previous element at that index.
- E remove(int index) - Deletes the element at the specified index, shifting all subsequent elements one index to the left, reducing the list’s size by one, and returning the removed element.
Java allows the generic ArrayList<E>, where the generic type E specifies the type of element.
When ArrayList<E> is specified, the types of the reference parameters and return type when using the methods are type E.
ArrayList<E> is preferred over ArrayList because it allows the compiler to find errors that would otherwise be found at runtime.

Size of the `ArrayList`

int size(); : Returns the number of elements in the list.

Consider the following code:

ArrayList<Integer> a1 = new ArrayList<>();
System.out.println(a1.size());

Adding Items to an `ArrayList`

boolean add(E obj); : Appends obj to the end of the list and returns true.
void add(int index, E obj) : Inserts obj at position index, as long as index is within the list’s length. It moves each element in the list 1 index higher and adds 1 to the list’s size.

Consider the following code:

ArrayList<Double> a2 = new ArrayList<>();
a2.add(1.0);
a2.add(2.0);
a2.add(3.0);
a2.add(1, 4.0);
System.out.println(a2);

[1.0, 4.0, 2.0, 3.0]

Let’s Look at an Example

Consider the following code:

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

h.add("Hello");
h.add("Hello");
h.add("HeLLO");
h.add("Hello");
h.add(1, "Hola");

h.add(26.2);
h.add(new String("Hello"));
h.add(false);
System.out.println(h);

Now, consider this code:

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

g.add("Hello");
g.add("Hello");
g.add("HeLLO");
g.add("Hello");
g.add(1, "Hola");

g.add(new String("Hello"));

System.out.println(g);

[Hello, Hola, Hello, HeLLO, Hello, Hello]

Question: Why does this code work?: The code works because it is valid Java code that uses an ArrayList to store and manipulate a list of strings. The output of the code is the nonsensical list of strings that includes the elements you added, with “Hola” inserted at index 1.

Deleting Items from an `ArrayList`

E remove(int index) : Removes the element at position index, and moves the elements at position index + 1 and higher to the left. It also subtracts one from the list’s size. The return value is the element formerly at position index.

// If you are confused of what list g is, look back at the previous code.
g.remove(3);
String former = g.remove(0);
System.out.println(former);

Hello

Updating Items in an `ArrayList`

E set(int index, E obj) : Replaces the element at position index with obj and returns the element formerly at position index.

String helloFormer = g.set(1, "Bonjour");
System.out.println(helloFormer);
System.out.println(g);

Hello
[Hola, Bonjour, Hello, Hello]

Accessing Items in an `ArrayList`

E get(int index) Returns the element at position index in the list.

String hello = g.get(3);
System.out.println(hello);
System.out.println(g);

Hello
[Hola, Bonjour, Hello, Hello]

Passing an `ArrayList` as a Method Parameter

The only time that it is wise to use ArrayList instead of ArrayList<E> is when it is as a function parameter and it is only using ArrayList<>.get(E) or ArrayList<>.size(). Consider the following code:

private void accessOnly(ArrayList arr) {
    if (arr.size() > 0) {
        System.out.println(arr.get(0)); // Change the index to the one you want to access
    } else {
        System.out.println("Array is empty");
    }
}

ArrayList<Integer> myList = new ArrayList<Integer>();
accessOnly(myList);

Array is empty

Returning an `ArrayList` from a Method

In order for you to return an ArrayList, the data type must be specified, and the return type must be the same as the return value. Consider the following code:

private ArrayList<String> returnTheSame() {
    ArrayList<String> arr = new ArrayList<String>(); // Initialize the ArrayList
    arr.add("Hello");
    return arr;
}

ArrayList<String> result = returnTheSame();
System.out.println(result);

[Hello]

Hacks

The learning objective is that “Students will be able to represent collections of related object reference data using ArrayList objects.” What does this mean to you?
Answer the following questions:
- Look back at Size of the ArrayList. What does the code output and why? This code is the output to the above ArrayList algorithms.
- Look back at Adding items to an ArrayList. What does the code output and why? What type of function is void, and what will be the return value? Void is a function type that returns nothing.
- Look back at Example 1. What two lines did we remove? Why? We removed the two lines because they had no impact on the functionality of the ArrayList.
- If an ArrayList is being used as a parameter, what are the only two methods I can use from it? What would happen if I tried to use any other methods? The get index and size methods are the only two methods you can use from it. If you tried any other methods, you would get a compiler error.
Using the Hack Helper, write code that will:
- Add 2 items to the list.
- Remove an item from the list anywhere of the user’s choice.
- Replace am item anywhere in the list of the user’s choice.
- Get the first and last element of the list, no matter the length.
- Return the items added, removed, replaced, and the list’s size, in one string.

Hack Helper

import java.util.ArrayList;

public class ArrayListMethodsExample {
    private String manipulateList() {
        ArrayList<Integer> nums = new ArrayList<>();

        // Add 2 items to the list
        nums.add(10);
        nums.add(20);

        // Remove an item from the list (index provided by the user)
        int removeIndex = 1; // You can change this index as per the user's choice
        String removedItem = "";
        if (removeIndex >= 0 && removeIndex < nums.size()) {
            removedItem = nums.remove(removeIndex).toString();
        }

        // Replace an item in the list (index and new value provided by the user)
        int replaceIndex = 0; // You can change this index as per the user's choice
        int newValue = 30;    // You can change this value as per the user's choice
        String replacedItem = "";
        if (replaceIndex >= 0 && replaceIndex < nums.size()) {
            replacedItem = nums.set(replaceIndex, newValue).toString();
        }

        // Get the first and last elements of the list (no matter the length)
        Integer firstElement = nums.isEmpty() ? null : nums.get(0);
        Integer lastElement = nums.isEmpty() ? null : nums.get(nums.size() - 1);

        // Return the items added, removed, replaced, and the list's size in one string
        int listSize = nums.size();
        return "Added: 10, 20; " +
               "Removed: " + removedItem + "; " +
               "Replaced: " + replacedItem + "; " +
               "List Size: " + listSize + "; " +
               "First Element: " + firstElement + "; " +
               "Last Element: " + lastElement;
    }

    public static void main(String[] args) {
        ArrayListMethodsExample example = new ArrayListMethodsExample();
        String output = example.manipulateList();
        System.out.println(output);
    }
}

ArrayListMethodsExample.main(null);

Added: 10, 20; Removed: 20; Replaced: 10; List Size: 1; First Element: 30; Last Element: 30

7.3: Traversing Arraylists

Learning Objectives:

With an Arraylist you can traverse objects using a for or while loop.
Traversing objects is similar to iterating through objects.

Essential Knowledge:

Iteration statements can be used to accsess all the elements in an Arraylist. This is called traversing the Arraylist.
Deleting elements during a traversal of an Arraylist requires special techniques to avoid skiping elements. This is called traversing the Arraylist.
The indicies of an Arraylist start at 0; If you try to use any value lower than 0, you will get an ArrayIndexOutOfBoundsException error

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

public class Main {
    public static void main(String[] args) {
        ArrayList<String> roster = new ArrayList<>();
        roster.add("Hello");
        roster.add("World");
        roster.add("Java");
        
        int sum = 0;
        for (int i = 0; i < roster.size(); i++) {
            String element = roster.get(i);
            if (element != null) {
                sum += element.length();
            }
        }
        System.out.println(sum);
    }
}

Breakdown:

We are first declaring a new arraylist and adding a few elements.
Next, we set the “sum” variable as 0.
We set a for loop to traverse through the arraylist, iterating through all the indices in the arraylist and adding up the lengths of all the values.
Lastly, we print it out.

Loop Conditions:

There are a few diffrent loop conditions you can use to traverse an Arraylist:

First, there are three major parts of a for loop: Initialisation, in which you declare the index, can be modified to change where you want to traverse from.

Boolean condition, in which you declare the stop condition, can be modified in order to change the index you want to stop traversing in.

Update, in which you declare how many indexes to go through, can be modified to skip certain indicies and traverse in a certain direction.

Practice:

Suppose we have an arraylist named grades, and we want to remove the entries that are lower than 70. replace the question marks with code to solve the problem:

import java.util.ArrayList;
import java.util.Iterator;

public class Main {
    public static void main(String[] args) {
        ArrayList<Double> grades = new ArrayList<>();
        grades.add(68.0);
        grades.add(71.0);
        grades.add(100.0);
        grades.add(80.0);

        // Use an Iterator to safely remove elements
        Iterator<Double> iterator = grades.iterator();
        while (iterator.hasNext()) {
            Double grade = iterator.next();
            if (grade < 70.0) {
                iterator.remove();
            }
        }

        System.out.println(grades);
    }
}

Main.main(null);

[71.0, 100.0, 80.0]

Using Enhanced For-Loop With Traversing:

Using Enhanced for loop is easier to read and write and is also more concise and avoids errors.
Indexes are not explicitly used and copies of the current element are made at each iteration.

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

public class Main {
    public static void main(String[] args) {
        List<String> roster = new ArrayList<>();
        roster.add("Hello");
        roster.add("World");
        roster.add("Java");

        // Using an enhanced for loop to iterate through the ArrayList
        for (String element : roster) {
            System.out.println(element);
        }
    }
}

Common mistakes:

Using the Wrong Data Type: Ensure that you declare your ArrayList with the correct data type. Using the wrong data type can lead to type mismatches and errors.
Incorrect Indexing: Be cautious when using a standard for loop. Off-by-one errors or accessing elements that don’t exist can lead to runtime exceptions.
Modifying the List During Iteration: Modifying an ArrayList (adding or removing elements) while iterating over it can lead to a ConcurrentModificationException. To avoid this, use an Iterator or create a copy of the list if modifications are needed.
Not Checking for Null Elements: When using enhanced for loops or iterators, check for null elements if there’s a possibility that your list contains them to avoid NullPointerExceptions.
Inefficient Searching: If you need to find a specific element, avoid using a linear search within a loop. Use appropriate methods like contains() or indexOf() to find elements efficiently.

Hacks:

Create a scenario which requires the use of arraylist traversal and create code to solve it.
Extra points to creative scenarios
90% credit to any working code and scenario
80% credit to incomplete code if you provide explanation of it
-10% deduction for late submition

import java.util.ArrayList;
import java.util.Scanner;

class Book {
    private String title;
    private String author;
    private int isbn;

    public Book(String title, String author, int isbn) {
        this.title = title;
        this.author = author;
        this.isbn = isbn;
    }

    public String getTitle() {
        return title;
    }

    public String getAuthor() {
        return author;
    }

    public int getIsbn() {
        return isbn;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public void setIsbn(int isbn) {
        this.isbn = isbn;
    }
}

public class LibraryManagementSystem {
    public static void main(String[] args) {
        ArrayList<Book> library = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.println("Library Book Management:");
            System.out.println("1. Add Book");
            System.out.println("2. Remove Book");
            System.out.println("3. Update Book Information");
            System.out.println("4. Display Book Collection");
            System.out.println("5. Exit");
            System.out.print("Enter your choice: ");
            int choice = scanner.nextInt();
            scanner.nextLine(); // Consume newline

            switch (choice) {
                case 1:
                    System.out.print("Enter book title: ");
                    String bookTitle = scanner.nextLine();
                    System.out.print("Enter book author: ");
                    String bookAuthor = scanner.nextLine();
                    System.out.print("Enter ISBN: ");
                    int isbn = scanner.nextInt();
                    scanner.nextLine();
                    Book newBook = new Book(bookTitle, bookAuthor, isbn);
                    library.add(newBook);
                    System.out.println("Book added to the collection.");
                    break;

                case 2:
                    System.out.print("Enter the ISBN of the book to remove: ");
                    int isbnToRemove = scanner.nextInt();
                    scanner.nextLine();
                    for (Book book : library) {
                        if (book.getIsbn() == isbnToRemove) {
                            library.remove(book);
                            System.out.println("Book removed from the collection.");
                            break;
                        }
                    }
                    break;

                case 3:
                    System.out.print("Enter the ISBN of the book to update: ");
                    int isbnToUpdate = scanner.nextInt();
                    scanner.nextLine();
                    for (Book book : library) {
                        if (book.getIsbn() == isbnToUpdate) {
                            System.out.print("Enter new book title: ");
                            String newTitle = scanner.nextLine();
                            System.out.print("Enter new book author: ");
                            String newAuthor = scanner.nextLine();
                            System.out.print("Enter new ISBN: ");
                            int newIsbn = scanner.nextInt();
                            scanner.nextLine();
                            book.setTitle(newTitle);
                            book.setAuthor(newAuthor);
                            book.setIsbn(newIsbn);
                            System.out.println("Book information updated.");
                            break;
                        }
                    }
                    break;

                case 4:
                    System.out.println("Library Book Collection:");
                    for (Book book : library) {
                        System.out.println("Title: " + book.getTitle() + ", Author: " +
                                book.getAuthor() + ", ISBN: " + book.getIsbn());
                    }
                    break;

                case 5:
                    System.out.println("Exiting the program.");
                    scanner.close();
                    System.exit(0);
                    break;

                default:
                    System.out.println("Invalid choice. Please try again.");
                    break;
            }
        }
    }
}

Book.main(null);

7.4: Developing Algorithms Using ArrayLists

Learning Objectives

In the context of ArrayList objects, this module aims to teach the following skills:

a. Iterating through ArrayLists using for or while loops.

b. Iterating through ArrayLists using enhanced for loops.

In the realm of algorithms, within the context of specific requirements that demand the utilization of ArrayList traversals, students will be able to:

Recognize established algorithms.
Customize existing algorithms.
Create new algorithms.

Essential Knowledge

Iteration statements provide a means to access all the elements stored within an ArrayList. This process is referred to as “traversing the ArrayList.”
The following methods related to ArrayLists, their functions, and appropriate use are covered in the Java Quick Reference:
- int size() - Returns the count of elements within the list.
- boolean add(E obj) - Appends the object obj to the end of the list and returns true.
- void add(int index, E obj) - Inserts obj at the specified index, shifting elements at and above that position to the right (incrementing their indices by 1) and increasing the list’s size by 1.
- E get(int index) - Retrieves the element at the given index in the list.
- E set(int index, E obj) - Replaces the element at the specified index with obj and returns the previous element at that index.
- E remove(int index) - Deletes the element at the specified index, shifting all subsequent elements one index to the left, reducing the list’s size by one, and returning the removed element.
There exist established algorithms for ArrayLists that make use of traversals to:
- Insert elements.
- Remove elements.
- Apply the same algorithms commonly used with 1D arrays.

Let’s Look at an Example (Example 1)

public class ArrayListExample {
    private double findMax(double[] values) {
         double max = values[0];
    
        for (int index = 1; index < values.length; index++) {
            if (values[index] > max) {
                max = values[index];
           }
        }
    
        return max;
    }
    
    public static void main(String[] args) {
        double[] nums = {1.0, 3.0, 2.0, 2.0, 1.0, 69.0, 2.0, 4.0, 6.0, 2.0, 5.0, 10.0};
        ArrayListExample example = new ArrayListExample();
        double max = example.findMax(nums);
        System.out.println("Maximum value: " + max);
    }
}

ArrayListExample.main(null);

Maximum value: 69.0

Take a closer look at the findMax() method. It takes in a list of doubles as parameters. It will then use a for loop to find the maximum value in the list. Now, using what we know, can we replace the list of doubles with an ArrayList of Doubles? We sure can! Take a look at how we can use ArrayList to do just that:

public class ArrayListExample {
    private double findMax(ArrayList<Double> values) {
        // double max = values.get(0);
    
        //for (int index = 1; index < values.size(); index++) {
        //    if (values.get(index) > max) {
        //        max = values.get(index);
        //    }
        //}
    
        //return max;
    }
    
    public static void main(String[] args) {
        ArrayList<Double> nums = new ArrayList<>();
        nums.add(1.0);
        nums.add(3.0);
        nums.add(2.0);
        nums.add(2.0);
        nums.add(1.0);
        nums.add(69.0);
        nums.add(2.0);
        nums.add(4.0);
        nums.add(6.0);
        nums.add(2.0);
        nums.add(5.0);
        nums.add(10.0);
        
        ArrayListExample example = new ArrayListExample();
        double max = example.findMax(nums);
        System.out.println("Maximum value: " + max);
    }
}

ArrayListExample.main(null);

Let’s Look at an Example (Example 2)

Take a look at this code:

public class ArrayListExample {
    private int findMin(int[] values) {
        //int min = Integer.MAX_VALUE;
        //for (int currentValue : values) {
        //    if (currentValue < min) {
        //        min = currentValue;
        //    }
        //}
        return min;
    }

    public static void main(String[] args) {
        int[] nums = {420, 703, 2034, 582, 1047, 4545};
        ArrayListExample example = new ArrayListExample();
        int min = example.findMin(nums);
        System.out.println("Minimum value: " + min);
    }
}

ArrayListExample.main(null);

Now, can we use ArrayLists to make this code better? We sure can! Take a look at the new and improved code that uses ArrayLists:

public class ArrayListExample {
    private int findMin(ArrayList<Integer> values) {
        //int min = Integer.MAX_VALUE;
        //for (int currentValue : values) {
        //    if (currentValue < min) {
        //        min = currentValue;
        //    }
        //}
        return min;
    }

    public static void main(String[] args) {
        ArrayList<Integer> nums = new ArrayList<>();
        nums.add(420);
        nums.add(703);
        nums.add(2034);
        nums.add(582);
        nums.add(1047);
        nums.add(4545);
        ArrayListExample example = new ArrayListExample();
        int min = example.findMin(nums);
        System.out.println("Minimum value: " + min);
    }
}

ArrayListExample.main(null);

Hacks

Answer the questions:
- Look back at the examples. What’s similar? What’s different? One example contains an ArrayList while the other one does not.
- Why do we use ArrayList? Why not just regular lists? We use them as they are easy to access and manipulate.
Demonstrate at least two ArrayList methods that aren’t ArrayList<>.size() and ArrayList<>.get().
Write the method findSum() using the Hack Helper and incorporating ArrayList.

import java.util.ArrayList;

public class ArrayListExample1 {
    public static void main(String[] args) {
        // Create an ArrayList of strings
        ArrayList<String> colors = new ArrayList<>();

        // Add elements to the ArrayList using the add() method
        colors.add("Red");
        colors.add("Green");
        colors.add("Blue");
        colors.add("Yellow");

        // Display the ArrayList
        System.out.println("Original ArrayList: " + colors);

        // Remove an element using the remove() method
        colors.remove("Green");

        // Display the modified ArrayList
        System.out.println("Updated ArrayList: " + colors);
    }
}

ArrayListExample1.main(null);

// used add and remove methods boy

Original ArrayList: [Red, Green, Blue, Yellow]
Updated ArrayList: [Red, Blue, Yellow]

import java.util.ArrayList;

public class ArrayListExample2 {
    public static int findSum(ArrayList<Integer> numbers) {
        int sum = 0;
        for (Integer number : numbers) {
            sum += number;
        }
        return sum;
    }

    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        int totalSum = findSum(numbers);
        System.out.println("The sum of the numbers is: " + totalSum);
    }
}

ArrayListExample2.main(null);

The sum of the numbers is: 60

Hack Helper

7.5 Searching

Learning Objectives

Apply sequential/linear search algorithms to search for specific information in array or arraylist objects

Essential Knowledge:

Sequential/linear search alogorithms check each element in order untill the desired value is found or all elementsin the array or arraylist have been checked

Search Process

Linear searching fits a standard for loop perfectly! We need to specify each element, one at a time, and do not need to track the index after execution
Inside the for loop, we retrieve the value from the structure at the specified index and compare it to the searched value
If it matches we return the index, otherwise we keep looking!

Searching Linear Structures

Finding information with a computer is something we need to know how to do. Linear search algorithms are BEST used when we do not have any idea about the order of the data and so we need to look at each element to determine if what we are looking for is in fact inside the array or `ArrayList`.

When searching, we do need to remember that different data types require comparisons!

When looking at int values, the == operator is the tool to use!
When searching for a double value, we need to make sure the value is close enough by doing some math!
Object instances should always use the .equals(otheThing) method to check for a match!

Searching an `ArrayList` of Double

public int where(double magicNumber, ArrayList<Double> realNumbers, double delta)
{
    for (int index = 0; index < realNumbers.size(); index++)
    {
        if (Math.abs(magicNumber - realNumbers.get(index)) < delta)
        {
            return index;
        }
    }
    return -1;
}

Explanation

The where function searches through a list of numbers to find and return the position of the first number that is very close to a specific target number, known as magicNumber. If no number in the list is close enough to the target number, the function returns -1, indicating that no match was found.

Searching an `ArrayList` of book for a `String`

public int findTheWord(String searchedPhrase, ArrayList<Book> myBooks)
{
    for (int index = 0; index < myBooks.size(); index++)
    {
        Book currentBook = myBooks.get(index);
        String currentPhrase = currentBook.getDescription();
        if(currentPhrase.equals(searchedPhrase))
        {
            return index;
        }
    }
    return -1;
}

Explanation

This little code snippet is like a treasure hunt through a collection of books; it’s on a mission to find the one book whose description matches exactly with a special phrase you’re looking for. If it finds the perfect match, it’ll excitedly tell you where it is in the collection, but if not, it’ll sadly let you know with a -1 that the search was a bust.

Questions

Should we use == when looking for an Object?

No, we should not use == to compare objects for equality in Java; instead, we should use the .equals() method to compare their content or references for reference equality.

Why did we subtract the double values?

We subtracted the double values to ensure that the lack of precision that is in the data type is handled within our code.

Why does order sometimes matter?

When searching for a value to remove from a list, if we search forward we have to make sure to adjust the loop control variable, or we might skip what we are looking for when removing!

7.6 Sorting

Learning Objectives

Apply selection sort and insertion sort algorithms to sort the elements of array or ArrayList objects.

Essential Knowledge:

Selection sort and insertion sort are iterative sorting algorithms that can be used to sort elements in an array or ArrayList.

Selection Sort

This is one of the easiest sorts to demonstrate. The selection sort identifies either the maximum or minimum of the compared values and iterates over the structure checking if the item stored at the index matches that condition, if so, it will swap the value stored at that index and continue. This implementation uses a helper method to perform the swap operation since variables can hold only one value at a time!

Example:

// with normal arrays
for (int outerLoop = 0; outerLoop < myDucks.length; outerLoop ++)
{
    int minIndex = outerLoop;
    for (int inner = outerLoop +1; inner < myDucks.length; inner++)
    {
        if (myDucks[inner].compareT(myDucks[minIndex]) < 0)
        {
            minIndex = inner;
        }
    }
    if (minIndex != outerLoop)
    {
        swapItems(minIndex, outerloop, myDucks);
    }
}

// with array lists
for (int outerLoop = 0; outerLoop < myDucks.size(); outerLoop++) {
    int minIndex = outerLoop;
    for (int inner = outerLoop + 1; inner < myDucks.size(); inner++) 
    {
        if (myDucks.get(inner).compareT(myDucks.get(minIndex)) < 0) 
        {
            minIndex = inner;
        }
    }
    if (minIndex != outerLoop) {
        swapItems(minIndex, outerLoop, myDucks); 
    }
}
/*
This code performs a selection sort on the myDucks ArrayList, ordering its elements based on the compareT method. 
During each iteration of the outer loop, it finds the index of the minimum element in the unsorted portion of the list and swaps it with the first element of the unsorted portion.
 */ 

Insertion Sort Algorithm

The insertion sort is characterized by building a sorted structure as it proceeds. It inserts each value it finds at the appropriate location in the data structure. This is often accomplished by using a while loop as the inner loop.

Example:

for (int outer = 1; outer < randomList.size(); outer++)
{
    DebugDuck tested = randomList.get(outer);
    int inner = outer -1;

    while ( innter >= 0 && tested.compareTo(randomList.get(inner)) < 0)
    {
        ramdomList.set(inner +1, randomList.get(inner));
        inner--;
    }
    randomList.set(inner +1, tested)
}
// This code arranges a list of DebugDuck objects in order using the insertion sort method, 
// by moving through the list and putting each item in its proper place one by one.

7.7: Ethical Issues around Data Collection

Learning Objectives:

Explaining the risks of privacy from collecting and storing personal data on computer systems.

Essential Knowledge:

When using the computer, personal privacy is at risk. Programmers should attempt to safeguard personal privacy.

Privacy Protection:

A simple way to protect privacy is to delete personal user info after done using it.
Another way is to minimize the amount of data used by the program in order to protect privacy.
Anonymizing personal data via the object method hashCode() is another way.

Hacks:

Think of other ways to safeguard user privacy (any other method not listed is fine)
Extra points to creative solutions
90% credit to any solution
80% credit to incomplete solution (how did you do that?)
-10% deduction for late submition

POWERSHELL SCRIPT TO ENFORCE FIREWALL ON A WINDOWS OS

If (-NOT ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator))
{
  # Relaunch as an elevated process:
  Start-Process powershell.exe "-File",('"{0}"' -f $MyInvocation.MyCommand.Path) -Verb RunAs
  exit
}

netsh advfirewall export "C:\Main\modules\firewallexport.wfw"

netsh advfirewall import "C:\Main\modules\firewall.wfw"

pause 

Write-Host Scan through firewall and firewall rules and remove anything suspicious

firewall.cpl

pause 

Write-Host "Profiles and Profiles Settings"
#Turning on Firewall for all Profiles
Netsh advfirewall set allprofiles state on

#Block Inbound and Allow Outbound for all Profiles, Block all inbound on public profile
Netsh advfirewall set allprofiles firewallpolicy blockinbound,allowoutbound
netsh advfirewall set publicprofile firewallpolicy blockinboundalways,allowoutbound

#Log Dropped and Allowed Connections
netsh advfirewall set allprofiles logging droppedconnections enable
netsh advfirewall set allprofiles logging allowedconnections enable

#Log Firewall
Set-NetFirewallProfile -all -LogMaxSizeKilobytes 10240 -LogAllowed true -LogBlocked true -notifyonlisten true

#Notifications
netsh advfirewall set allprofiles settings inboundusernotification enable

#Unicast Response
netsh advfirewall set allprofiles settings unicastresponsetomulticast disable

# Disable Merge of Gpedit Rules with Local Firewall Rules for Public Profile
reg add HKLM\SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile /v AllowLocalPolicyMerge /t REG_DWORD /d 0 /f

# $registryPath = "HKLM\SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile"
# $Name = "AllowLocalPolicyMerge"
# $value = "0"
# IF(!(Test-Path $registryPath))
#   {
#     New-Item -Path $registryPath -Force | Out-Null
#     New-ItemProperty -Path $registryPath -Name $name -Value $value `
#     -PropertyType DWORD -Force | Out-Null}
# ELSE {
#     New-ItemProperty -Path $registryPath -Name $name -Value $value `
#     -PropertyType DWORD -Force | Out-Null}

# Disable Merge of Local Connection Rules with Gpedit Settings
reg add HKLM\SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile /v AllowLocalIPsecPolicyMerge /t REG_DWORD /d 0 /f

# $registryPath = "HKLM\SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile"
# $Name = "AllowLocalIPsecPolicyMerge"
# $value = "0"
# IF(!(Test-Path $registryPath))
#   {
#     New-Item -Path $registryPath -Force | Out-Null
#     New-ItemProperty -Path $registryPath -Name $name -Value $value `
#     -PropertyType DWORD -Force | Out-Null}
# ELSE {
#     New-ItemProperty -Path $registryPath -Name $name -Value $value `
#     -PropertyType DWORD -Force | Out-Null}

# Disable IPV6 Redirects 
netsh interface ipv6 set global icmpredirects=disabled

# Configuring Manually the Default Current Hop Limit
netsh interface ipv6 set global defaultcurhoplimit=64

# Disable ISATAP
netsh interface ipv6 isatap set state disabled

# Disable Teredo
netsh interface ipv6 set teredo type=disabled

# Disable 6to4
netsh interface ipv6 6to4 set state disabled

# Set the MTU, Disable Router Discovery and Minimize DAD Transmits Per Interface
# netsh  interface  ipv6  set  interface  "1"  mtu=1280  dadtransmits=0 routerdiscovery=disabled

pause

I went above and beyond man..

Grading:

7.2 Hacks (0.19)
7.3 Hacks (0.19)
7.4 Hacks (0.19)
7.7 Hacks (0.19)
Popcorn Hacks (0.19)
Anything else creative or above-and-beyond showing your understanding of ArrayLists (0.05)

Unit 7 • 81 min read

Description

Unit 7: ArrayList

7.1: ArrayList Intro

Quick lil popcorn hack

7.2: ArrayList Methods

Learning Objectives

Essential Knowledge

Size of the ArrayList

Adding Items to an ArrayList

Let’s Look at an Example

Deleting Items from an ArrayList

Updating Items in an ArrayList

Accessing Items in an ArrayList

Passing an ArrayList as a Method Parameter

Returning an ArrayList from a Method

Hacks

Hack Helper

7.3: Traversing Arraylists

Learning Objectives:

Essential Knowledge:

Breakdown:

Loop Conditions:

Practice:

Using Enhanced For-Loop With Traversing:

Common mistakes:

Hacks:

7.4: Developing Algorithms Using ArrayLists

Learning Objectives

Essential Knowledge

Let’s Look at an Example (Example 1)

Let’s Look at an Example (Example 2)

Hacks

Hack Helper

7.5 Searching

Learning Objectives

Essential Knowledge:

Search Process

Searching Linear Structures

Finding information with a computer is something we need to know how to do. Linear search algorithms are BEST used when we do not have any idea about the order of the data and so we need to look at each element to determine if what we are looking for is in fact inside the array or ArrayList.

When searching, we do need to remember that different data types require comparisons!

Searching an ArrayList of Double

Explanation

Searching an ArrayList of book for a String

Explanation

Questions

Should we use == when looking for an Object?

Why did we subtract the double values?

Why does order sometimes matter?

When searching for a value to remove from a list, if we search forward we have to make sure to adjust the loop control variable, or we might skip what we are looking for when removing!

7.6 Sorting

Learning Objectives

Essential Knowledge:

Selection Sort

Insertion Sort Algorithm

7.7: Ethical Issues around Data Collection

Learning Objectives:

Essential Knowledge:

Privacy Protection:

Hacks:

Grading:

Size of the `ArrayList`

Adding Items to an `ArrayList`

Deleting Items from an `ArrayList`

Updating Items in an `ArrayList`

Accessing Items in an `ArrayList`

Passing an `ArrayList` as a Method Parameter

Returning an `ArrayList` from a Method

Finding information with a computer is something we need to know how to do. Linear search algorithms are BEST used when we do not have any idea about the order of the data and so we need to look at each element to determine if what we are looking for is in fact inside the array or `ArrayList`.

Searching an `ArrayList` of Double

Searching an `ArrayList` of book for a `String`