Introduction to ArrayList

An ArrayList in Java is a part of the Java Collections Framework and is a resizable array implementation of the List interface. Unlike arrays, ArrayList can dynamically grow and shrink in size. It provides more flexibility in terms of adding, removing, and accessing elements.

Key Features of ArrayList

Dynamic Size: Automatically resizes itself when elements are added or removed.
Indexed Access: Allows fast random access to elements using an index.
Non-Synchronized: Not thread-safe by default, but can be synchronized externally.
Allows Duplicates: Can store duplicate elements.
Maintains Insertion Order: Elements are stored in the order they are inserted.

Creating an ArrayList

To use ArrayList, you need to import it from the java.util package.

import java.util.ArrayList;

public class ArrayListExample {
    public static void main(String[] args) {
        // Creating an ArrayList of Strings
        ArrayList<String> fruits = new ArrayList<>();

        // Adding elements to the ArrayList
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");

        // Printing the ArrayList
        System.out.println(fruits);
    }
}

Explanation

Import Statement: import java.util.ArrayList; imports the ArrayList class.
Creating an ArrayList: ArrayList<String> fruits = new ArrayList<>(); creates an ArrayList to store String elements.
Adding Elements: fruits.add("Apple"); adds elements to the ArrayList.
Printing the ArrayList: System.out.println(fruits); prints the elements of the ArrayList.

Common Methods of ArrayList

Here are some commonly used methods of the ArrayList class:

Method	Description
`add(E e)`	Appends the specified element to the end of the list.
`add(int index, E element)`	Inserts the specified element at the specified position in the list.
`get(int index)`	Returns the element at the specified position in the list.
`set(int index, E element)`	Replaces the element at the specified position in the list with the specified element.
`remove(int index)`	Removes the element at the specified position in the list.
`size()`	Returns the number of elements in the list.
`clear()`	Removes all elements from the list.
`isEmpty()`	Returns `true` if the list contains no elements.
`contains(Object o)`	Returns `true` if the list contains the specified element.

Practical Examples

Example 1: Basic Operations

import java.util.ArrayList;

public class ArrayListOperations {
    public static void main(String[] args) {
        ArrayList<String> fruits = new ArrayList<>();

        // Adding elements
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");

        // Accessing elements
        System.out.println("First fruit: " + fruits.get(0));

        // Modifying elements
        fruits.set(1, "Mango");
        System.out.println("Modified list: " + fruits);

        // Removing elements
        fruits.remove(2);
        System.out.println("After removal: " + fruits);

        // Checking size
        System.out.println("Size of the list: " + fruits.size());

        // Checking if list contains an element
        System.out.println("Contains 'Apple': " + fruits.contains("Apple"));

        // Clearing the list
        fruits.clear();
        System.out.println("List after clearing: " + fruits.isEmpty());
    }
}

Explanation

Adding Elements: Adds "Apple", "Banana", and "Orange" to the ArrayList.
Accessing Elements: Retrieves the first element using get(0).
Modifying Elements: Changes the second element to "Mango" using set(1, "Mango").
Removing Elements: Removes the third element using remove(2).
Checking Size: Prints the size of the ArrayList using size().
Checking Containment: Checks if "Apple" is in the list using contains("Apple").
Clearing the List: Clears all elements using clear() and checks if the list is empty using isEmpty().

Practical Exercises

Exercise 1: Basic ArrayList Operations

Task: Create an ArrayList of integers, add five integers to it, and perform the following operations:

Print the ArrayList.
Retrieve and print the third element.
Change the second element to a new value.
Remove the fourth element.
Print the final ArrayList.

Solution:

import java.util.ArrayList;

public class ArrayListExercise {
    public static void main(String[] args) {
        ArrayList<Integer> numbers = new ArrayList<>();

        // Adding elements
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);
        numbers.add(40);
        numbers.add(50);

        // Printing the ArrayList
        System.out.println("Original list: " + numbers);

        // Retrieving and printing the third element
        System.out.println("Third element: " + numbers.get(2));

        // Changing the second element
        numbers.set(1, 25);
        System.out.println("After modification: " + numbers);

        // Removing the fourth element
        numbers.remove(3);
        System.out.println("After removal: " + numbers);
    }
}

Exercise 2: ArrayList of Custom Objects

Task: Create a class Student with fields id and name. Create an ArrayList of Student objects, add three students to it, and perform the following operations:

Print the ArrayList.
Retrieve and print the name of the student with the second id.
Change the name of the student with the first id.
Remove the student with the third id.
Print the final ArrayList.

Solution:

import java.util.ArrayList;

class Student {
    int id;
    String name;

    Student(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{id=" + id + ", name='" + name + "'}";
    }
}

public class StudentArrayList {
    public static void main(String[] args) {
        ArrayList<Student> students = new ArrayList<>();

        // Adding students
        students.add(new Student(1, "Alice"));
        students.add(new Student(2, "Bob"));
        students.add(new Student(3, "Charlie"));

        // Printing the ArrayList
        System.out.println("Original list: " + students);

        // Retrieving and printing the name of the student with the second id
        System.out.println("Student with second id: " + students.get(1).name);

        // Changing the name of the student with the first id
        students.get(0).name = "Alicia";
        System.out.println("After modification: " + students);

        // Removing the student with the third id
        students.remove(2);
        System.out.println("After removal: " + students);
    }
}

Conclusion

In this section, we covered the basics of ArrayList in Java, including its key features, common methods, and practical examples. We also provided exercises to help reinforce the concepts. Understanding ArrayList is crucial for working with dynamic collections of data in Java, and it serves as a foundation for more advanced data structures and algorithms. In the next section, we will explore LinkedList, another important data structure in the Java Collections Framework.

ArrayList

Introduction to ArrayList

Key Features of ArrayList

Creating an ArrayList

Explanation

Common Methods of ArrayList

Practical Examples

Example 1: Basic Operations

Explanation

Practical Exercises

Exercise 1: Basic ArrayList Operations

Exercise 2: ArrayList of Custom Objects

Conclusion

Java Programming Course

Module 1: Introduction to Java

Module 2: Control Flow

Module 3: Object-Oriented Programming

Module 4: Advanced Object-Oriented Programming

Module 5: Data Structures and Collections

Module 6: Exception Handling

Module 7: File I/O

Module 8: Multithreading and Concurrency

Module 9: Networking

Module 10: Advanced Topics

Module 11: Java Frameworks and Libraries

Module 12: Building Real-World Applications