Introduction to Low Level Design

Low level design is a crucial step in software development that involves designing the intricate details of the system architecture and implementation. It focuses on breaking down the high-level requirements and specifications into detailed and implementable modules, classes, and functions.

As a senior engineer with a strong background in Java development, Spring Boot, MySQL, and AWS, you are well-equipped to dive into the world of low level design. Think of low level design as the backbone of a software application, where you have the opportunity to apply your expertise in creating efficient, scalable, and maintainable solutions.

To illustrate the importance of low level design, let's consider a simple example. Imagine you are tasked with implementing a payment app. Low level design would involve defining the problem statement, identifying the requirements, creating a class diagram to visualize the relationships between different components, establishing entity relationships, designing the database schema, and selecting the appropriate design pattern to ensure code reusability and flexibility.

As an engineer experienced in Java, you can leverage your programming skills to implement the low level design of the payment app. Let's take a look at a Java code snippet that demonstrates the classic "FizzBuzz" problem:

1  class Main {
2    public static void main(String[] args) {
3    // replace with your Java logic here
4    for(int i = 1; i <= 100; i++) {
5      if(i % 3 == 0 && i % 5 == 0) {
6          System.out.println("FizzBuzz");
7      } else if(i % 3 == 0) {
8          System.out.println("Fizz");
9      } else if(i % 5 == 0) {
10          System.out.println("Buzz");
11      } else {
12          System.out.println(i);
13      }
14    }
15  }

In this code snippet, we use a for loop to iterate from 1 to 100. For numbers divisible by both 3 and 5, we print "FizzBuzz". For numbers divisible by 3, we print "Fizz", and for numbers divisible by 5, we print "Buzz". For all other numbers, we simply print the number itself. This simple example showcases how low level design requires attention to detail and the ability to translate requirements into a working implementation.

By mastering the principles and practices of low level design, you will be able to architect robust and efficient software solutions. Are you ready to delve deeper into the world of low level design and elevate your software development skills?

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class Main {

    public static void main(String[] args) {

    // replace with your Java logic here

    for(int i = 1; i <= 100; i++) {

      if(i % 3 == 0 && i % 5 == 0) {

          System.out.println("FizzBuzz");

      } else if(i % 3 == 0) {

          System.out.println("Fizz");

      } else if(i % 5 == 0) {

          System.out.println("Buzz");

      } else {

          System.out.println(i);

      }

    }

  }

}

Defining the Problem Statement

In the process of low level design, the first step is to define the problem statement. This involves identifying and documenting the requirements and objectives of the payment app design.

To better understand this step, let's consider an example problem statement for designing a payment app:

1  // Define the problem statement
2  String problemStatement = "Design a payment app that allows users to make secure online transactions.";
3
4  // Define the requirements
5  String[] requirements = {
6    "1. Users should be able to create an account and login.",
7    "2. Users should be able to add and manage multiple payment methods.",
8    "3. Users should be able to initiate and complete transactions.",
9    "4. Transactions should be secure and encrypted.",
10    "5. Users should receive notifications for successful transactions."
11  };
12
13  // Print the problem statement
14  System.out.println("Problem Statement:");
15  System.out.println(problemStatement);
16
17  // Print the requirements
18  System.out.println("Requirements:");
19  for (String requirement : requirements) {
20    System.out.println("- " + requirement);
21  }

In this example, we define the problem statement as designing a payment app that allows users to make secure online transactions. The requirements for this app include allowing users to create an account and login, add and manage multiple payment methods, initiate and complete transactions, ensure secure and encrypted transactions, and provide notifications for successful transactions.

Defining a clear problem statement and documenting the requirements is essential in the low level design process. It helps set the direction and goals for designing the payment app and ensures that all stakeholders have a clear understanding of what needs to be achieved.

Next, we will move on to creating the class diagram, which visualizes the relationships between different components in the payment app.

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class Main {

  public static void main(String[] args) {

    // replace with your Java logic here

    // Define the problem statement

    String problemStatement = "Design a payment app that allows users to make secure online transactions.";

​

    // Define the requirements

    String[] requirements = {

      "1. Users should be able to create an account and login.",

      "2. Users should be able to add and manage multiple payment methods.",

      "3. Users should be able to initiate and complete transactions.",

      "4. Transactions should be secure and encrypted.",

      "5. Users should receive notifications for successful transactions."

    };

​

    // Print the problem statement

    System.out.println("Problem Statement:");

    System.out.println(problemStatement);

​

    // Print the requirements

    System.out.println("Requirements:");

    for (String requirement : requirements) {

      System.out.println("- " + requirement);

    }

  }

}

Creating the Class Diagram

One of the key components of low level design is creating the class diagram. The class diagram provides a visual representation of the classes and their relationships in the payment app.

To create the class diagram, we need to identify the classes that are part of the payment app and define their relationships. In this example, let's consider three main classes in the payment app: User, PaymentMethod, and Transaction.

1class User {
2  // class fields and methods
3}
4
5class PaymentMethod {
6  // class fields and methods
7}
8
9class Transaction {
10  // class fields and methods
11}

In this class diagram, we have three classes: User, PaymentMethod, and Transaction. These classes represent the main entities in the payment app. Each class can have its own attributes and methods.

Next, we need to define the relationships between these classes. For example, a user can have multiple payment methods, so we can define a one-to-many relationship between the User and PaymentMethod classes:

1paymentApp.addRelationship("User", "PaymentMethod", "one-to-many");

Similarly, a user can have multiple transactions, so we can define a one-to-many relationship between the User and Transaction classes:

1paymentApp.addRelationship("User", "Transaction", "one-to-many");

Once we have defined the classes and their relationships, we can generate the class diagram using a class diagram generator. The generated class diagram provides a visual representation of the classes and their relationships in the payment app.

1ClassDiagramGenerator generator = new ClassDiagramGenerator();
2String classDiagram = generator.generate(paymentApp);

Here's an example of a generated class diagram:

1Class Diagram:
2
3  +----------------+                  +-------------------+
4  |      User      |    <--------    |   PaymentMethod   |
5  +----------------+                  +-------------------+
6  |                |                  |                   |
7  |                |                  |                   |
8  |                |                  |                   |
9  +----------------+                  +-------------------+
10       ^                                               |
11       |                                               |
12 +-----+                                               |
13 |                                                      |
14 |                                                      |
15 V                                                      V
16+-----------------+                              +----------------+
17|   Transaction   |                              |   AnotherClass |
18+-----------------+                              +----------------+

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class Main {

  public static void main(String[] args) {

    // create an instance of a class

    PaymentApp paymentApp = new PaymentApp();

    // add classes to the payment app

    paymentApp.addClass(new User());

    paymentApp.addClass(new PaymentMethod());

    paymentApp.addClass(new Transaction());

    // create relationships between classes

    paymentApp.addRelationship("User", "PaymentMethod", "one-to-many");

    paymentApp.addRelationship("User", "Transaction", "one-to-many");

    // generate the class diagram

    ClassDiagramGenerator generator = new ClassDiagramGenerator();

    String classDiagram = generator.generate(paymentApp);

    // print the class diagram

    System.out.println("Class Diagram:");

    System.out.println(classDiagram);

  }

}

Establishing Entity Relationships

In low level design, it is important to define the relationships between different entities in the payment app. This helps us understand how the entities are related to each other and how they interact.

Let's consider the example of the User and PaymentMethod entities in the payment app. A user can have multiple payment methods, so we need to establish a relationship between these entities.

In the database schema, we can represent this relationship using foreign keys. The User table will have a primary key column (ID) and the PaymentMethod table will have a foreign key column (User_ID) that references the ID column in the User table.

Here's an example of the database schema representation:

User Table: +----+------------------+ | ID | Username | +----+------------------+ | 1 | john@example.com | +----+------------------+

PaymentMethod Table: +----+-----------+---------+ | ID | User_ID | Method | +----+-----------+---------+ | 1 | 1 | Credit | | 2 | 1 | Debit | +----+-----------+---------+

In the PaymentMethod table, the User_ID column references the ID column in the User table, establishing the one-to-many relationship between the User and PaymentMethod entities.

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// Establishing Entity Relationships

  // In the payment app, we have multiple entities that are related to each other. Let's define the relationships between these entities.

  // One of the relationships is between the User and PaymentMethod entities.

  // A user can have multiple payment methods, so it's a one-to-many relationship.

  // We can represent this relationship using foreign keys in the database.

  // Here's an example of how we can define the relationship in the database schema:

  // User Table

  // +----+------------------+

  // | ID |     Username     |

  // +----+------------------+

  // | 1  | john@example.com |

  // +----+------------------+

  // PaymentMethod Table

  // +----+-----------+---------+

  // | ID | User_ID   | Method  |

  // +----+-----------+---------+

  // | 1  | 1         | Credit  |

  // | 2  | 1         | Debit   |

  // +----+-----------+---------+

  // We can see that the User_ID in the PaymentMethod table references the ID column in the User table.

  // This establishes the one-to-many relationship between the User and PaymentMethod entities.

Designing the Database Schema

In the low level design of the payment app, one crucial step is designing the database schema. The database schema represents the structure of the payment app's database and defines the relationships between different entities.

To design the database schema, we need to consider the requirements of the payment app and identify the entities that need to be stored in the database. For example, the payment app might have entities such as User, PaymentMethod, Transaction, and Discount.

Once we have identified the entities, we can define the attributes and relationships for each entity. For example, the User entity might have attributes such as ID, Name, and Email, and a relationship with the PaymentMethod entity indicating that a user can have multiple payment methods.

Here's an example of a database schema for the payment app:

1User Table:
2+----+--------------+------------------+
3| ID |     Name     |      Email       |
4+----+--------------+------------------+
5| 1  | John Doe     | john@example.com |
6| 2  | Jane Smith   | jane@example.com |
7+----+--------------+------------------+
8
9PaymentMethod Table:
10+----+---------+----------------+---------+
11| ID | User_ID |    Method      | Default |
12+----+---------+----------------+---------+
13| 1  | 1       | Credit Card    |    1    |
14| 2  | 1       | Debit Card     |    0    |
15| 3  | 2       | PayPal         |    1    |
16+----+---------+----------------+---------+
17
18Transaction Table:
19+----+---------------+-------------+---------------------+
20| ID | User_ID       | Amount      |    Timestamp        |
21+----+---------------+-------------+---------------------+
22| 1  | 1             | 100.00      | 2022-01-01 10:00:00 |
23| 2  | 2             | 50.00       | 2022-01-02 15:30:00 |
24+----+---------------+-------------+---------------------+

This database schema reflects the relationships between the User, PaymentMethod, and Transaction entities. The User table has a primary key column (ID) and the PaymentMethod table has a foreign key column (User_ID) that references the ID column in the User table. Similarly, the Transaction table has a foreign key column (User_ID) that references the ID column in the User table.

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class Main {

    public static void main(String[] args) {

    // replace with your Java logic here

    for(int i = 1; i <= 100; i++) {

      if(i % 3 == 0 && i % 5 == 0) {

          System.out.println("FizzBuzz");

      } else if(i % 3 == 0) {

          System.out.println("Fizz");

      } else if(i % 5 == 0) {

          System.out.println("Buzz");

      } else {

          System.out.println(i);

      }

    }    

  }

}

Exploring Design Patterns

When it comes to designing software, it's important to leverage design patterns to solve recurring problems and improve the overall structure and maintainability of the codebase. Design patterns are proven solutions that have been developed and refined over time by experienced software engineers.

Let's explore some common design patterns that can be applied in the low level design of the payment app:

Singleton Pattern

The Singleton pattern ensures that a class has only one instance and provides a global point of access to it. In the context of the payment app, we can use the Singleton pattern to ensure that there is only one instance of the PaymentApp class throughout the application lifecycle.

Here's an example of how the Singleton pattern can be implemented in Java:

1// Singleton Class
2final class PaymentApp {
3  // Private constructor to prevent instantiation
4  private PaymentApp() {}
5
6  // Create a single instance of PaymentApp
7  private static PaymentApp instance = new PaymentApp();
8
9  // Get the single instance of PaymentApp
10  public static PaymentApp getInstance() {
11    return instance;
12  }
13
14  // Other methods and logic
15}

In the above code, the PaymentApp class has a private constructor to prevent direct instantiation. The class also declares a static instance variable which holds the single instance of the class. The getInstance() method returns the single instance of the PaymentApp class, allowing other parts of the code to access it.

Other Design Patterns

Apart from the Singleton pattern, there are many other design patterns that can be explored and applied in the low level design of the payment app. Some commonly used patterns include:

• Factory Pattern: Used to create objects without specifying the exact class of object that will be created.
• Strategy Pattern: Defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime.
• Observer Pattern: Defines a one-to-many dependency between objects, so that when one object changes state, all its dependents are notified and updated accordingly.

These are just a few examples, and there are many more design patterns available for different scenarios. It's important to understand the principles behind each pattern and choose the appropriate one based on the specific requirements of the payment app.

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class Main {

  public static void main(String[] args) {

    // Replace with your Java logic here

    // For example, let's use the Singleton design pattern

    PaymentApp paymentApp = PaymentApp.getInstance();

    paymentApp.processPayment();

  }

}

​

final class PaymentApp {

  // Private constructor to prevent instantiation

  private PaymentApp() {}

​

  // Create a single instance of PaymentApp

  private static PaymentApp instance = new PaymentApp();

​

  // Get the single instance of PaymentApp

  public static PaymentApp getInstance() {

    return instance;

  }

​

  public void processPayment() {

    // Implement the logic to process the payment

    System.out.println("Processing payment...");

    // Your code here

  }

}

Implementing Code in Java

Now that we have designed the low level structure of the payment app using various techniques such as defining the problem statement, creating the class diagram, establishing entity relationships, and designing the database schema, it's time to implement the actual code.

As a Java developer with good knowledge in Spring Boot, MySQL, and AWS, you are well-equipped to write the code for the payment app. Let's look at a simple example of how you can implement the payment app logic using the Java programming language.

1class Main {
2  public static void main(String[] args) {
3    // replace with your Java logic here
4    for(int i = 1; i <= 100; i++) {
5      if(i % 3 == 0 && i % 5 == 0) {
6          System.out.println("FizzBuzz");
7      } else if(i % 3 == 0) {
8          System.out.println("Fizz");
9      } else if(i % 5 == 0) {
10          System.out.println("Buzz");
11      } else {
12          System.out.println(i);
13      }
14    }
15  }
16}

In the above code snippet, we have a main method which serves as the entry point of the program. Inside the main method, we have a loop that iterates from 1 to 100. For each iteration, we check if the current number is divisible by both 3 and 5, in which case we print "FizzBuzz". If it is only divisible by 3, we print "Fizz", and if it is only divisible by 5, we print "Buzz". For all other numbers, we simply print the number itself.

This is just a simple example to demonstrate implementing code in Java. In the actual payment app, you would need to write code for various functionalities such as handling user input, performing calculations, interacting with databases, and integrating with external systems.

As you continue learning low level design and implementing code in Java, you will gain more hands-on experience and become more proficient in building robust and efficient software systems.

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class Main {

  public static void main(String[] args) {

    // replace with your Java logic here

    for(int i = 1; i <= 100; i++) {

      if(i % 3 == 0 && i % 5 == 0) {

          System.out.println("FizzBuzz");

      } else if(i % 3 == 0) {

          System.out.println("Fizz");

      } else if(i % 5 == 0) {

          System.out.println("Buzz");

      } else {

          System.out.println(i);

      }

    }    

  }

}