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());

• 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);

• 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);

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);

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.