Low level design is a crucial aspect of software development, especially when it comes to building complex systems like a payment application. It involves breaking down the high-level requirements and problem statements into smaller components and designing the structure and behavior of each component.

In low level design, we focus on the implementation details of the system. It includes defining the entities and their relationships, creating class diagrams to visualize the class structure, and designing the database schema to store the data.

To start with low level design for a payment app, we first need to analyze the problem statements and identify the requirements. This helps in understanding the functionalities the app needs to perform and the data it needs to handle.

Once the requirements are clear, we can start creating a class diagram. A class diagram illustrates the relationships between classes, their attributes, and methods. It helps in understanding the overall structure of the application.

After designing the class diagram, we define the entities and their relationships in the system. Entities represent the real-world objects that the app interacts with, and their relationships define how these objects are connected.

Next, we move on to designing the database schema. The database schema defines the structure of the database, including tables, columns, and relationships between tables. It determines how the data is organized and accessed.

Throughout the low level design process, we also need to consider the design patterns that can be applied to improve the overall design of the application. Design patterns are proven solutions to common design problems, and they help in making the design more maintainable, scalable, and flexible.

Once the low level design is complete, we can proceed with the code implementation. In this course, we'll be implementing a payment app using low level design principles in Java. The implementation will include writing code to handle the functionalities defined during the low level design process.

Now that we have a high-level overview of low level design, let's dive deeper into each step and understand the concepts and techniques involved.