Java ArrayList add() Method

The ArrayList.add() method in Java is used to add elements to an ArrayList. This guide will cover the usage of both overloaded versions of this method, explain how they work, and provide examples to demonstrate their functionality. Additionally, we will cover a real-world use case to illustrate its application.

Table of Contents

1. Introduction
2. add Method Syntax
   • add(E e)
   • add(int index, E element)
3. How They Work
4. Examples
   • Adding an Element to the End of the List
   • Adding an Element at a Specific Position
   • Handling IndexOutOfBoundsException
5. Real-World Use Case
6. Conclusion

Introduction

The ArrayList class in Java is part of the java.util package and provides a resizable array implementation. The add() method is a fundamental operation that allows you to add elements to the list. This method comes in two forms: one that appends an element to the end of the list, and another that inserts an element at a specified position.

add Method Syntax

add(E e)

The syntax for the add(E e) method is as follows:

public boolean add(E e)

• e: The element to be appended to the end of the list.
• The method returns true if the element is added successfully.

add(int index, E element)

The syntax for the add(int index, E element) method is as follows:

public void add(int index, E element)

• index: The index at which the specified element is to be inserted.
• element: The element to be inserted.

How They Work

add(E e)

When you use add(E e), the method appends the specified element to the end of the ArrayList. Internally, it checks if there is enough capacity to add the new element. If not, it increases the capacity of the ArrayList. The method then adds the element to the next available position and increments the size of the list.

add(int index, E element)

When you use add(int index, E element), the method inserts the specified element at the specified position in the ArrayList. Internally, it checks if the index is within the bounds of the list (0 to size of the list). If the index is valid, it shifts the existing elements from the specified index onwards to the right to make space for the new element. Then, it inserts the element at the specified index and increments the size of the list.

Examples

Adding an Element to the End of the List

The add(E e) method appends the specified element to the end of the ArrayList.

Example

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

public class AddExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");

        System.out.println("ArrayList: " + list);
    }
}

Output:

ArrayList: [Apple, Banana, Orange]

Adding an Element at a Specific Position

The add(int index, E element) method inserts the specified element at the specified position in the ArrayList.

Example

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

public class AddAtIndexExample {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");
        list.add(1, "Grapes");

        System.out.println("ArrayList: " + list);
    }
}

Output:

ArrayList: [Apple, Grapes, Banana, Orange]

Handling IndexOutOfBoundsException

If the specified index is out of range, the add(int index, E element) method throws an IndexOutOfBoundsException.

Example

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

public class AddWithExceptionHandling {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Orange");

        try {
            list.add(5, "Grapes"); // This will throw an exception
        } catch (IndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Error: Index: 5, Size: 3

Real-World Use Case

Task Management System

In a task management system, tasks are often added to a list as they are created. The ArrayList.add() method can be used to add new tasks to the list. If tasks need to be prioritized, you can insert them at specific positions in the list.

Example

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

class Task {
    String name;
    boolean isHighPriority;

    Task(String name, boolean isHighPriority) {
        this.name = name;
        this.isHighPriority = isHighPriority;
    }

    @Override
    public String toString() {
        return name + (isHighPriority ? " (High Priority)" : "");
    }
}

public class TaskManager {
    public static void main(String[] args) {
        List<Task> tasks = new ArrayList<>();

        // Add tasks to the list
        tasks.add(new Task("Write report", false));
        tasks.add(new Task("Prepare presentation", false));

        // Add a high priority task at the beginning
        tasks.add(0, new Task("Fix critical bug", true));

        // Display all tasks
        System.out.println("Task List:");
        tasks.forEach(task -> System.out.println(task));
    }
}

Output:

Task List:
Fix critical bug (High Priority)
Write report
Prepare presentation

Conclusion

The ArrayList.add() method in Java is a versatile tool for adding elements to a list. By understanding how to use both forms of this method, you can effectively manage the contents of an ArrayList in various scenarios, including real-world applications like task management systems. Whether you are appending elements to the end of the list or inserting them at specific positions, the add() method provides a straightforward and efficient solution.