Java design pattern classification and interpretation of principles

Java design patterns are divided into three categories: creational, structural and behavioral, and follow the principles of single responsibility, open-closed, dependency inversion and interface isolation. Practical cases include: singleton pattern (creation type), adapter pattern (structural type) and strategy pattern (behavioral type). Design patterns provide proven code reuse solutions that help develop flexible and scalable code.

Java design pattern classification and interpretation of principles

Introduction

Design pattern is A proven code reuse solution for common software development problems. They allow developers to create code that is flexible, maintainable, and easily extensible. Java provides a rich set of built-in design patterns for solving various problems.

Classification

Java design patterns are divided into three categories according to their focus:

• Creational patterns: Used to create objects. For example, factory method pattern, singleton pattern.
• Structural pattern: Used to combine and associate objects. For example, adapter mode, bridge mode.
• Behavioral pattern: Used to manage interactions between objects. For example, observer pattern, strategy pattern.

Principles

When applying design patterns, it is crucial to follow the following principles:

• Single Responsibility Principle : Each class should have only one primary responsibility.
• Open-closed principle: Open to extensions, closed to modifications.
• Dependency inversion principle: High-level modules should not depend on low-level modules, both should depend on abstractions.
• Interface isolation principle: Interfaces should be as granular as possible, specifying only necessary operations.

Practical case

Single case mode(Creative mode)

The singleton mode ensures that a class only has An instance. This is typically used to create global resources or configuration objects.

public class Singleton {

    private static Singleton instance = null;

    private Singleton() { }

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

Adapter pattern (structural pattern)

The adapter pattern allows incompatible interfaces to work together. For example, integrating old systems with new ones.

interface Target {
    void operation();
}

class Adaptee {
    void specificOperation() { }
}

class Adapter implements Target {

    private Adaptee adaptee;

    public Adapter(Adaptee adaptee) {
        this.adaptee = adaptee;
    }

    @Override
    public void operation() {
        adaptee.specificOperation();
    }
}

Strategy Mode (Behavioral Mode)

Strategy Mode allows algorithms to be exchanged at runtime. This is used to implement customizable or extensible systems.

interface Strategy {
    int calculate(int a, int b);
}

class AdditionStrategy implements Strategy {

    @Override
    public int calculate(int a, int b) {
        return a + b;
    }
}

class SubtractionStrategy implements Strategy {

    @Override
    public int calculate(int a, int b) {
        return a - b;
    }
}

class Context {

    private Strategy strategy;

    public Context(Strategy strategy) {
        this.strategy = strategy;
    }

    public void executeStrategy(int a, int b) {
        System.out.println(strategy.calculate(a, b));
    }
}

Conclusion

Design patterns are powerful tools in Java development, and they provide a proven approach to solving common software development problems. By understanding the classifications and principles, developers can effectively apply design patterns to create flexible, maintainable, and scalable code.

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