Contact Management System in Java

Introduction

A Contact Management System is a practical Java project that demonstrates core programming concepts such as object-oriented design, collections, file I/O, user input validation, and CRUD operations (Create, Read, Update, Delete). This console-based application allows users to manage personal or professional contacts with details like name, phone number, email, and address. The system persists data to a file (contacts.csv) for durability across sessions and provides a menu-driven interface for intuitive interaction.

Features

Add contacts with name, phone, email, and address
View all contacts in a formatted list
Search contacts by name or phone number
Update existing contacts
Delete contacts
Save contacts to CSV file on exit
Load contacts from CSV file on startup
Input validation for phone numbers and emails
Menu-driven console interface

Complete Source Code

1. Contact.java – Contact Model Class

// Contact.java public class Contact { private String name; private String phone; private String email; private String address; public Contact(String name, String phone, String email, String address) { this.name = name; this.phone = phone; this.email = email; this.address = address; } // Getters public String getName() { return name; } public String getPhone() { return phone; } public String getEmail() { return email; } public String getAddress() { return address; } // Setters public void setName(String name) { this.name = name; } public void setPhone(String phone) { this.phone = phone; } public void setEmail(String email) { this.email = email; } public void setAddress(String address) { this.address = address; } @Override public String toString() { return String.format("Name: %s%nPhone: %s%nEmail: %s%nAddress: %s%n", name, phone, email, address); } // CSV format: name,phone,email,address public String toCSV() { return String.format("%s,%s,%s,%s", name, phone, email, address); } public static Contact fromCSV(String csvLine) { String[] parts = csvLine.split(",", 4); // Split into 4 parts max if (parts.length == 4) { return new Contact(parts[0], parts[1], parts[2], parts[3]); } return null; } }

2. ContactManager.java – Core Logic Class

// ContactManager.java import java.io.*; import java.nio.file.Files; import java.nio.file.Paths; import java.util.*; public class ContactManager { private List<Contact> contacts; private static final String FILE_NAME = "contacts.csv"; public ContactManager() { this.contacts = new ArrayList<>(); loadContacts(); } public void addContact(String name, String phone, String email, String address) { contacts.add(new Contact(name, phone, email, address)); System.out.println("Contact added successfully."); } public void viewAllContacts() { if (contacts.isEmpty()) { System.out.println("No contacts found."); return; } for (int i = 0; i < contacts.size(); i++) { System.out.println((i + 1) + ".\n" + contacts.get(i)); } } public void searchContacts(String query) { boolean found = false; query = query.toLowerCase(); for (Contact contact : contacts) { if (contact.getName().toLowerCase().contains(query) || contact.getPhone().contains(query)) { System.out.println(contact); found = true; } } if (!found) { System.out.println("No contacts found matching: " + query); } } public void updateContact(int index, String name, String phone, String email, String address) { if (isValidIndex(index)) { Contact contact = contacts.get(index); contact.setName(name); contact.setPhone(phone); contact.setEmail(email); contact.setAddress(address); System.out.println("Contact updated successfully."); } else { System.out.println("Invalid contact number."); } } public void deleteContact(int index) { if (isValidIndex(index)) { contacts.remove(index); System.out.println("Contact deleted."); } else { System.out.println("Invalid contact number."); } } private boolean isValidIndex(int index) { return index >= 0 && index < contacts.size(); } public void saveContacts() { try (PrintWriter writer = new PrintWriter(new FileWriter(FILE_NAME))) { for (Contact contact : contacts) { writer.println(contact.toCSV()); } System.out.println("Contacts saved to " + FILE_NAME); } catch (IOException e) { System.err.println("Error saving contacts: " + e.getMessage()); } } private void loadContacts() { if (!Files.exists(Paths.get(FILE_NAME))) return; try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) { String line; while ((line = reader.readLine()) != null) { Contact contact = Contact.fromCSV(line); if (contact != null) { contacts.add(contact); } } System.out.println("Loaded " + contacts.size() + " contacts from " + FILE_NAME); } catch (IOException e) { System.err.println("Error loading contacts: " + e.getMessage()); } } }

3. InputValidator.java – Utility Class for Validation

// InputValidator.java import java.util.regex.Pattern; public class InputValidator { private static final String PHONE_PATTERN = "^\\+?[0-9]{10,15}$"; private static final String EMAIL_PATTERN = "^[a-zA-Z0-9_+&*-]+(?:\\.[a-zA-Z0-9_+&*-]+)*@" + "(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,7}$"; public static boolean isValidPhone(String phone) { return Pattern.matches(PHONE_PATTERN, phone.trim()); } public static boolean isValidEmail(String email) { return Pattern.matches(EMAIL_PATTERN, email.trim()); } }

4. Main.java – Application Entry Point

// Main.java import java.util.Scanner; public class Main { public static void main(String[] args) { ContactManager manager = new ContactManager(); Scanner scanner = new Scanner(System.in); boolean running = true; System.out.println("=== Contact Management System ==="); while (running) { System.out.println("\nChoose an option:"); System.out.println("1. Add Contact"); System.out.println("2. View All Contacts"); System.out.println("3. Search Contact"); System.out.println("4. Update Contact"); System.out.println("5. Delete Contact"); System.out.println("6. Exit"); System.out.print("Enter your choice: "); String choice = scanner.nextLine().trim(); switch (choice) { case "1": addContact(scanner, manager); break; case "2": manager.viewAllContacts(); break; case "3": searchContact(scanner, manager); break; case "4": updateContact(scanner, manager); break; case "5": deleteContact(scanner, manager); break; case "6": manager.saveContacts(); System.out.println("Goodbye!"); running = false; break; default: System.out.println("Invalid choice. Please enter 1-6."); } } scanner.close(); } private static void addContact(Scanner scanner, ContactManager manager) { System.out.print("Enter name: "); String name = scanner.nextLine().trim(); if (name.isEmpty()) { System.out.println("Name cannot be empty."); return; } System.out.print("Enter phone: "); String phone = scanner.nextLine().trim(); if (!InputValidator.isValidPhone(phone)) { System.out.println("Invalid phone number. Use 10-15 digits (optional + prefix)."); return; } System.out.print("Enter email: "); String email = scanner.nextLine().trim(); if (!email.isEmpty() && !InputValidator.isValidEmail(email)) { System.out.println("Invalid email format."); return; } System.out.print("Enter address: "); String address = scanner.nextLine().trim(); manager.addContact(name, phone, email, address); } private static void searchContact(Scanner scanner, ContactManager manager) { System.out.print("Enter name or phone to search: "); String query = scanner.nextLine().trim(); if (!query.isEmpty()) { manager.searchContacts(query); } else { System.out.println("Search query cannot be empty."); } } private static void updateContact(Scanner scanner, ContactManager manager) { manager.viewAllContacts(); if (manager.contacts.isEmpty()) return; System.out.print("Enter contact number to update: "); if (!scanner.hasNextInt()) { System.out.println("Invalid input. Please enter a number."); scanner.nextLine(); // Clear invalid input return; } int index = scanner.nextInt() - 1; scanner.nextLine(); // Consume newline System.out.print("Enter new name: "); String name = scanner.nextLine().trim(); if (name.isEmpty()) { System.out.println("Name cannot be empty."); return; } System.out.print("Enter new phone: "); String phone = scanner.nextLine().trim(); if (!InputValidator.isValidPhone(phone)) { System.out.println("Invalid phone number."); return; } System.out.print("Enter new email: "); String email = scanner.nextLine().trim(); if (!email.isEmpty() && !InputValidator.isValidEmail(email)) { System.out.println("Invalid email format."); return; } System.out.print("Enter new address: "); String address = scanner.nextLine().trim(); manager.updateContact(index, name, phone, email, address); } private static void deleteContact(Scanner scanner, ContactManager manager) { manager.viewAllContacts(); if (manager.contacts.isEmpty()) return; System.out.print("Enter contact number to delete: "); if (!scanner.hasNextInt()) { System.out.println("Invalid input. Please enter a number."); scanner.nextLine(); // Clear invalid input return; } int index = scanner.nextInt() - 1; scanner.nextLine(); // Consume newline manager.deleteContact(index); } }

How It Works

1. Data Model

The Contact class encapsulates contact details and provides CSV serialization.
toCSV() and fromCSV() enable file persistence.

2. Core Logic

ContactManager handles all CRUD operations and file I/O.
Contacts are stored in an ArrayList<Contact> for dynamic management.

3. File Format

Data is stored in contacts.csv with comma-separated values:

 Alice,+1234567890,[email protected],123 Main St Bob,+0987654321,[email protected],456 Oak Ave

4. Validation

InputValidator uses regex to ensure:
Phone numbers: 10–15 digits, optional + prefix
Emails: Standard email format

5. User Interaction

Menu-driven interface with clear prompts.
Input validation prevents invalid data entry.
Graceful handling of empty lists and invalid indices.

Sample Output

=== Contact Management System === Loaded 1 contacts from contacts.csv Choose an option: 1. Add Contact 2. View All Contacts 3. Search Contact 4. Update Contact 5. Delete Contact 6. Exit Enter your choice: 2 1. Name: Alice Phone: +1234567890 Email: [email protected] Address: 123 Main St Choose an option: 1. Add Contact 2. View All Contacts 3. Search Contact 4. Update Contact 5. Delete Contact 6. Exit Enter your choice: 3 Enter name or phone to search: Alice Name: Alice Phone: +1234567890 Email: [email protected] Address: 123 Main St Choose an option: 1. Add Contact 2. View All Contacts 3. Search Contact 4. Update Contact 5. Delete Contact 6. Exit Enter your choice: 6 Contacts saved to contacts.csv Goodbye!

Key Concepts Demonstrated

Concept	Implementation
Object-Oriented Design	`Contact` class with encapsulation
Collections	`ArrayList<Contact>` for dynamic storage
File I/O	CSV read/write with `BufferedReader`/`PrintWriter`
User Input	`Scanner` with validation
CRUD Operations	Add, view, search, update, delete
Error Handling	Try-catch for I/O, input validation
Regular Expressions	Phone/email validation
Menu System	Loop with switch-case

Possible Enhancements

Unique ID generation: Add auto-incrementing contact IDs
Sorting: Sort contacts by name or other fields
Categories/Groups: Tag contacts (e.g., family, work)
GUI version: Use JavaFX or Swing
Database storage: Replace CSV with SQLite or MySQL
Import/Export: Support vCard (.vcf) format
Duplicate detection: Prevent adding identical contacts

Best Practices Applied

Single Responsibility: Each class has one clear purpose
Input validation: Prevents invalid data entry
Resource management: Scanner and file streams properly closed
Meaningful names: Clear variable and method names
Persistence: Data survives application restarts
User feedback: Clear success/error messages
Modular design: Separation of concerns (model, logic, UI)

Conclusion

This Contact Management System provides a comprehensive foundation for learning Java fundamentals while building a functional application. It demonstrates how to structure code using OOP principles, manage data with collections, persist state with file I/O, validate user input, and create an interactive user experience. The modular design makes it easy to extend with new features, and the error handling ensures robustness. Whether used as a learning exercise or a starting point for a more advanced address book application, this project reinforces core Java skills that are applicable to real-world development.