How to Build a Simple Contact Management System Using Collections in Java?

Introduction

In this tutorial, we will learn how to create a simple Contact Management System using Java collections. This system will store and manage information about contacts such as name, phone number, email address, and more. Collections, a core part of Java, provide a powerful and efficient way to store and manipulate data, and we’ll take full advantage of them in our application.

Understanding the Requirements

The Contact Management System we’re going to build needs to allow users to:

• Add a new contact
• View existing contacts
• Update contact information
• Delete contacts

We’ll use the Java collections framework to store contacts. Specifically, we’ll make use of the HashMap and ArrayList collections for efficient management and retrieval of contacts.

Step 1: Define the Contact Class

To represent a contact, we’ll create a simple Contact class. This class will store basic information such as name, phone number, and email address.

public class Contact {
    private String name;
    private String phoneNumber;
    private String email;

    // Constructor
    public Contact(String name, String phoneNumber, String email) {
        this.name = name;
        this.phoneNumber = phoneNumber;
        this.email = email;
    }

    // Getters and Setters
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Name: " + name + ", Phone: " + phoneNumber + ", Email: " + email;
    }
}
        

This class will hold the necessary details of a contact and provide getter and setter methods for manipulating the data. Additionally, we have overridden the toString() method to display contact details in a readable format.

Step 2: Set Up the Contact Manager Class

Next, we’ll create the ContactManager class, which will handle adding, viewing, updating, and deleting contacts. We’ll use a HashMap to store the contacts, where the contact’s name is used as the key and the Contact object is the value.

import java.util.HashMap;
import java.util.Map;

public class ContactManager {
    private Map contacts;

    // Constructor
    public ContactManager() {
        contacts = new HashMap<>();
    }

    // Add a contact
    public void addContact(Contact contact) {
        contacts.put(contact.getName(), contact);
        System.out.println("Contact added: " + contact);
    }

    // View a contact by name
    public void viewContact(String name) {
        Contact contact = contacts.get(name);
        if (contact != null) {
            System.out.println(contact);
        } else {
            System.out.println("Contact not found.");
        }
    }

    // Update a contact's information
    public void updateContact(String name, Contact updatedContact) {
        if (contacts.containsKey(name)) {
            contacts.put(name, updatedContact);
            System.out.println("Contact updated: " + updatedContact);
        } else {
            System.out.println("Contact not found.");
        }
    }

    // Delete a contact
    public void deleteContact(String name) {
        if (contacts.containsKey(name)) {
            contacts.remove(name);
            System.out.println("Contact deleted: " + name);
        } else {
            System.out.println("Contact not found.");
        }
    }
}
        

The ContactManager class manages a HashMap where the key is the contact name and the value is the Contact object. It contains methods to add, view, update, and delete contacts. The methods interact with the HashMap to perform the required operations efficiently.

Step 3: Test the Application

Now that we have both the Contact and ContactManager classes set up, let’s create a main method to test the application.

public class Main {
    public static void main(String[] args) {
        // Create a ContactManager instance
        ContactManager contactManager = new ContactManager();

        // Add contacts
        Contact contact1 = new Contact("Alice", "1234567890", "alice@example.com");
        contactManager.addContact(contact1);

        Contact contact2 = new Contact("Bob", "9876543210", "bob@example.com");
        contactManager.addContact(contact2);

        // View a contact
        contactManager.viewContact("Alice");

        // Update a contact
        Contact updatedContact = new Contact("Alice", "1112223333", "alice_new@example.com");
        contactManager.updateContact("Alice", updatedContact);

        // View the updated contact
        contactManager.viewContact("Alice");

        // Delete a contact
        contactManager.deleteContact("Bob");

        // Try to view the deleted contact
        contactManager.viewContact("Bob");
    }
}
        

In the main method, we create a ContactManager instance and perform several operations: adding contacts, viewing a contact, updating a contact, and deleting a contact. Each operation is displayed in the console for user feedback.

Output

Contact added: Name: Alice, Phone: 1234567890, Email: alice@example.com
Contact added: Name: Bob, Phone: 9876543210, Email: bob@example.com
Name: Alice, Phone: 1234567890, Email: alice@example.com
Contact updated: Name: Alice, Phone: 1112223333, Email: alice_new@example.com
Name: Alice, Phone: 1112223333, Email: alice_new@example.com
Contact deleted: Bob
Contact not found.
        

As shown, the program successfully adds, updates, and deletes contacts, with appropriate feedback at each step.

Conclusion

In this tutorial, we have successfully built a simple Contact Management System using Java collections. We used the HashMap to store contacts and implemented basic operations such as add, view, update, and delete. The use of collections makes it easy to manage and manipulate the contacts efficiently. You can further extend this application by adding more features like searching contacts by phone number or email, storing data in a database, or even creating a graphical user interface (GUI).