CSXiaotang Computer Science Notes

The Java Collections Framework provides data structures that allow for dynamic storage of an arbitrary number of elements, overcoming the fixed-size limitation of arrays which make additions and deletions inconvenient. The framework is primarily divided into three main interfaces: List, Set, and Map.

• List: An ordered collection that allows duplicate elements. Common implementations include ArrayList, LinkedList, and Vector.
• Set: A collection that contains no duplicate elements. Common implementations include HashSet and TreeSet.
• Map: An object that maps keys to values, where each key must be unique.

The static keyword in Java is applied in four primary contexts:

1. Static Variables: Fields shared by all instances of a class.
2. Static Methods: Methods that can be invoked without creating an instance of the class.
3. Static Code Blocks: Blocks of code that run once when the class is first loaded into memory.
4. Static Inner Classes: Nested classes that do not require a reference to an instance of the outer class.

MyBatis implements Object Relationship Mapping (ORM) to bridge Java entity classes and relational databases. The mapping relationship is as follows:

• Class maps to Table
• Property maps to Field/Column
• Object maps to Row

The three-tier architecture is a software design pattern used to separate concerns and maintainability in applications. It consists of the following layers:

1. Controller (Control Layer): Responsible for receiving requests from the frontend, processing the initial request, and returning the response data.
2. Service (Business Logic Layer): Responsible for implementing the specific business logic and rules of the application.
3. Dao (Data Access Object / Persistence Layer): Responsible for all data access operations, including Create, Read, Update, and Delete (CRUD) operations against the database.

Indexes in MySQL are data structures used to quickly locate rows with specific values, avoiding full table scans. The essence of an index is trading additional storage space (typically 2-3x) for significantly faster query speeds (100-1000x).

MySQL uses B+ trees to achieve this efficiency through four key design choices:

1. Low tree height (typically 3-4 layers/log n depth).
2. Leaf node linked lists for efficient range queries.
3. Page alignment.
4. Internal nodes store only pointers, not actual data records.

SpringMVC follows the Model-View-Controller (MVC) design pattern to separate concerns in a web application:

• Model (M): Classes responsible for processing data and business logic.
• View: The presentation layer that interacts with the end-user.
• Controller: The control layer that receives requests from the browser and returns responses.

A Service Registry (such as Nacos or Eureka) acts as a central directory that maintains the real-time status of all service instances in a microservices architecture. It solves the problem of hard-coding IP addresses and ports, allowing services to discover each other dynamically.

Core problems solved:

• Service Discovery: Callers dynamically obtain a list of provider addresses without hard-coding.
• Health Checking: Unhealthy instances are automatically removed via heartbeat mechanisms.
• Load Balancing Base: Provides a list of multiple instances that can be used for round-robin, random, or weighted request distribution.
• Elastic Scaling: New instances register automatically and offline instances are removed, making scaling transparent to the caller.
• Fault Isolation: If one instance fails, only its traffic is affected, not the entire system.