Software Design Patterns — Assignment 1 (AITU)

Overview

Two standalone tasks that demonstrate the SOLID principles in plain Java. The assignment is part of the Software Design Patterns course at Astana IT University.

• Task 1 — Payment Processing System: a small payment pipeline that accepts any payment method through a common interface, making it trivial to add new methods without touching existing code.
• Task 2 — Notification System: a multi-channel notification dispatcher (SMS, Email, Push, Slack) that also supports bulk delivery to a list of recipients.

Principles / Concepts implemented

• Single Responsibility Principle (SRP) — each class does exactly one thing: CreditCardPayment handles credit-card logic; PaymentProcessor handles dispatching; BulkNotificationSender handles iteration over recipients.
• Open/Closed Principle (OCP) — new payment methods (BankTransferPayment) and notification channels (SlackNotification) are added by implementing an interface, without modifying any existing class.
• Liskov Substitution Principle (LSP) — PaymentProcessor accepts any PaymentMethod; BulkNotificationSender accepts any NotificationChannel; all concrete implementations are interchangeable at those injection points.
• Interface Segregation Principle (ISP) — PaymentMethod exposes a single method (processPayment); NotificationChannel exposes a single method (sendNotification). No class is forced to implement methods it doesn't need.
• Dependency Inversion Principle (DIP) — high-level modules (PaymentProcessor, BulkNotificationSender) depend on abstractions (interfaces), not on concrete implementations.
• Polymorphism via interfaces — concrete classes (CreditCardPayment, SMSNotification, etc.) are treated uniformly through their interface type at call sites.

Project structure

src/
├── com/payment/
│   ├── PaymentMethod.java          # interface: processPayment(double)
│   ├── CreditCardPayment.java      # implements PaymentMethod
│   ├── PayPalPayment.java          # implements PaymentMethod
│   ├── BankTransferPayment.java    # implements PaymentMethod
│   ├── PaymentProcessor.java       # dispatches to any PaymentMethod
│   └── Main.java                   # demo: runs all three payment types
│
└── com/notification/
    ├── NotificationChannel.java    # interface: sendNotification(String, String)
    ├── SMSNotification.java        # implements NotificationChannel
    ├── EmailNotification.java      # implements NotificationChannel
    ├── PushNotification.java       # implements NotificationChannel
    ├── SlackNotification.java      # implements NotificationChannel
    ├── BulkNotificationSender.java # sends one message to a list of recipients
    └── Main.java                   # demo: bulk email, SMS, and push

How to run

Via command line (JDK 21+)

Task 1 — Payment:

cd src
javac com/payment/*.java
java com.payment.Main

Task 2 — Notification:

cd src
javac com/notification/*.java
java com.notification.Main

Via IntelliJ IDEA

1. Open the project root in IntelliJ IDEA.
2. The SDK is pre-configured to JDK 21 (see .idea/misc.xml).
3. Open either com/payment/Main.java or com/notification/Main.java and click Run.

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Adil Ormanov — GitHub