Unit 7 ArrayList P3

• 7.1 ARRAY LIST METHODS
• 7.2 ARRAY LIST METHODS

7.1 ARRAY LIST METHODS

• ArrayList is a resizeable array
• ArrayLists are dynamic meaning that its size can be altered as necessary
• 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
• To use an arrayList it is necessary to be imported from the java util package

VOCABULARY

Static: Once initialized, size cannot be changed (arrays)

Dynamic: Size of list can be changed at any time (arrayLists)

import java.util.ArrayList;  // Import the ArrayList class
// Declare and initialize an ArrayList of integers
ArrayList<Integer> numbersList = new ArrayList<>();
System.out.println(numbersList);

[]

• ArrayLists are created in a similar manner as other object classes
• in the <> when declaring an arrayList is the data type it will contain. (integer, string, etc…)
• Can also make an arraylist without declaring the data type but it can prevent error detection

ArrayList<String> wordList = new ArrayList<String>(); // with data type
ArrayList blankList = new ArrayList(); // without data type
System.out.println(wordList);

[]

7.2 ARRAY LIST METHODS

• You can get the number of items in an ArrayList using the .size() method
• All arrayLists start with 0

ArrayList<String> sizeList = new ArrayList<String>();
System.out.println(sizeList.size());

0

• You can add values to an array list by using add method. syntax: list.add(obj)

• How you would join the end of a line to buy a ticket (similar concept)

ArrayList<String> addList = new ArrayList<String>();
addList.add("CSA");
System.out.println(addList.size());
System.out.println(addList);

1
[CSA]

• 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, where the generic type E specifies the type of element.

• When ArrayList is specified, the types of the reference parameters and return type when using the methods are type E.

• ArrayList is preferred over ArrayList because it allows the compiler to find errors that would otherwise be found at runtime.

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

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

a2.remove(2.0);
System.out.println(a2);

0
[1.0, 2.0, 3.0]
[1.0, 3.0]

import java.util.ArrayList;
 // Create ArrayList of Integers
ArrayList<Integer> a1 = new ArrayList<>();
System.out.println("Initial size of a1: " + a1.size());

// Create ArrayList of Doubles and add elements
ArrayList<Double> a2 = new ArrayList<>();
a2.add(1.0);
a2.add(2.0);
a2.add(3.0);
System.out.println("Initial a2: " + a2);

// Remove element at index 2
a2.remove(2); // Use index for removal, not value
System.out.println("After removing element at index 2: " + a2);

// Insert element at index 1
a2.add(1, 1.5);
System.out.println("After inserting 1.5 at index 1: " + a2);

// Retrieve element at index 2
Double elementAtIndex2 = a2.get(2);
System.out.println("Element at index 2: " + elementAtIndex2);

// Replace element at index 1
Double previousElement = a2.set(1, 1.75);
System.out.println("After replacing element at index 1: " + a2);
System.out.println("Previous element at index 1: " + previousElement);

// Get the size of a2
int sizeOfA2 = a2.size();
System.out.println("Size of a2: " + sizeOfA2);

Initial size of a1: 0
Initial a2: [1.0, 2.0, 3.0]
After removing element at index 2: [1.0, 2.0]
After inserting 1.5 at index 1: [1.0, 1.5, 2.0]
Element at index 2: 2.0
After replacing element at index 1: [1.0, 1.75, 2.0]
Previous element at index 1: 1.5
Size of a2: 3

POPCORN HACKS 7.1 & 7.2 Create an ArrayList of Strings with the following elements: “Apple”, “Banana”, “Cherry”, “Date”, “Elderberry”. Complete the following tasks using the ArrayList methods you’ve learned:

• Task 1: Print the size of the ArrayList.
• Task 2: Add a new element “Fig” to the end of the list.
• Task 3: Insert “Grape” at index 2.
• Task 4: Replace the element at index 4 with “Guava”.
• Task 5: Remove the element at index 1.
• Task 6: Retrieve and print the element at index 3.

At the end of each task, print the current state of the ArrayList to verify the result.

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Create an ArrayList of Strings
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Cherry");
        fruits.add("Date");
        fruits.add("Elderberry");

        // Task 1: Print the size of the ArrayList
        System.out.println("Task 1: Size of the ArrayList: " + fruits.size());
        System.out.println("Current ArrayList: " + fruits);

        // Task 2: Add a new element "Fig" to the end of the list
        fruits.add("Fig");
        System.out.println("Task 2: Added 'Fig'");
        System.out.println("Current ArrayList: " + fruits);

        // Task 3: Insert "Grape" at index 2
        fruits.add(2, "Grape");
        System.out.println("Task 3: Inserted 'Grape' at index 2");
        System.out.println("Current ArrayList: " + fruits);

        // Task 4: Replace the element at index 4 with "Guava"
        fruits.set(4, "Guava");
        System.out.println("Task 4: Replaced element at index 4 with 'Guava'");
        System.out.println("Current ArrayList: " + fruits);

        // Task 5: Remove the element at index 1
        fruits.remove(1);
        System.out.println("Task 5: Removed element at index 1");
        System.out.println("Current ArrayList: " + fruits);

        // Task 6: Retrieve and print the element at index 3
        String elementAtIndex3 = fruits.get(3);
        System.out.println("Task 6: Element at index 3: " + elementAtIndex3);
    }
}
ArrayListExample.main(null);

Task 1: Size of the ArrayList: 5
Current ArrayList: [Apple, Banana, Cherry, Date, Elderberry]
Task 2: Added 'Fig'
Current ArrayList: [Apple, Banana, Cherry, Date, Elderberry, Fig]
Task 3: Inserted 'Grape' at index 2
Current ArrayList: [Apple, Banana, Grape, Cherry, Date, Elderberry, Fig]
Task 4: Replaced element at index 4 with 'Guava'
Current ArrayList: [Apple, Banana, Grape, Cherry, Guava, Elderberry, Fig]
Task 5: Removed element at index 1
Current ArrayList: [Apple, Grape, Cherry, Guava, Elderberry, Fig]
Task 6: Element at index 3: Guava