Design Patterns and Programming Paradigms: Concepts, Architecture Patterns, and Practical Applications

Design patterns are reusable solutions to common software design problems, offering flexibility, elegance, and better reusability; they represent best practices for a class of problems.

The core challenges they address are reuse and decoupling, making unstable components depend on stable abstractions and enhancing adaptability to change.

Programming paradigms—structured programming, object‑oriented programming, and functional programming—are abstract concepts that influence how languages implement solutions. For example, C follows structured programming, Java is primarily object‑oriented (with lambda support since Java 8), and modern languages like Scala, Go, and Rust support multiple paradigms.

Design patterns can be implemented in any language, but language features affect their expression. Java’s Strategy pattern arose because earlier versions lacked first‑class functions, whereas JavaScript can pass functions directly without a separate strategy class.

class MyFile: def write(self): print('I write a message into file.') class MyDB: def write(self): print('I write data into db.') def doIt(writer): writer.write() def demo(): myFile = MyFile() myDB = MyDB() doIt(myFile) doIt(myDB)

Architecture patterns operate at a higher, macro level, defining system structure, communication interfaces, component models, and integration frameworks. Examples include Layered, Client‑Server, Master‑Slave, Pipe‑Filter, Broker, Peer‑to‑Peer, Event‑Bus, MVC, Blackboard, and Interpreter patterns, each with specific descriptions and applicable scenarios.

Design patterns are classified by purpose (creational, structural, behavioral) and scope (class vs. object). The 23 classic GoF patterns include Singleton, Factory Method, Abstract Factory, Builder, Prototype, Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy, Template Method, Strategy, Command, Chain of Responsibility, State, Observer, Mediator, Iterator, Visitor, Memento, and Interpreter.

Practical code examples demonstrate how to apply these patterns in a water‑fetching scenario:

public interface Waterable { Water getWater(); } public class TiaoShui implements Waterable { public Water getWater() { System.out.println("先到山下去！"); return "水是挑上来的！"; } } public class TaiShui implements Waterable { public Water getWater() { System.out.println("先到山下去！"); return "水是抬上来的！"; } } public class DengShui implements Waterable { public Water getWater() { System.out.println("就坐在原地！"); return "水是等不来的！"; } } public class Factory { public static Waterable getWaterable(Integer heShangNum) { switch (heShangNum) { case 1: return new TiaoShui(); case 2: return new TaiShui(); case 3: return new DengShui(); default: throw new RuntimeException("庙小，装不下那么多和尚！"); } } }

The Strategy pattern is illustrated by selecting the appropriate Waterable implementation based on the number of monks, while the Template Method pattern abstracts the common steps of fetching water:

public abstract class AbstractWaterable implements Waterable { @Override public Water getWater() { takeTool(); toRiver(); return moveWater(); } protected abstract String takeTool(); protected String toRiver() { System.out.println("走过去！"); return "步行"; } protected abstract Water moveWater(); }

Builder pattern constructs complex toolboxes for different fetching strategies, Proxy adds logging (e.g., "敲一下木鱼，打一次卡！"), Chain of Responsibility implements security checks (pet, dress code, noise), and Command pattern encapsulates daily tasks (breakfast, cleaning, ringing the bell) with support for undo/redo.

Design principles such as SRP, OCP, LSP, DIP, ISP, and LKP underpin these patterns, emphasizing low coupling, high cohesion, reusability, and extensibility. The article concludes that design patterns are not rigid rules but flexible solutions that, when combined with solid principles, help solve complex software problems efficiently.