Exploration and analysis of common interface design patterns

Explore common interface design patterns in Java

Introduction:
In software design, interface is one of the very important design patterns. The design of the interface can improve the readability, scalability and maintainability of the code. In the Java language, interface is one of the key elements. It provides a protocol and specification for communication between classes, which can help us better perform object-oriented programming.

This article will explore several common interface design patterns and provide specific code examples to help readers better understand and apply these design patterns.

1. Strategy Pattern
Strategy Pattern is a design pattern that defines a series of algorithms so that these algorithms can be replaced with each other at runtime. This pattern makes algorithm changes independent of the client using the algorithm.

Sample code:

// 定义策略接口
public interface Strategy {
    int doOperation(int num1, int num2);
}

// 实现策略接口的具体策略类
public class OperationAdd implements Strategy {
    public int doOperation(int num1, int num2) {
       return num1 + num2;
    }
}

public class OperationSubtract implements Strategy {
    public int doOperation(int num1, int num2) {
       return num1 - num2;
    }
}

// 使用策略的客户端
public class Context {
    private Strategy strategy;

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

    public int executeStrategy(int num1, int num2){
       return strategy.doOperation(num1, num2);
    }
}

// 测试示例
public class StrategyPatternTest {
    public static void main(String[] args) {
       Context context = new Context(new OperationAdd());
       System.out.println("10 + 5 = " + context.executeStrategy(10, 5));

       context = new Context(new OperationSubtract());
       System.out.println("10 - 5 = " + context.executeStrategy(10, 5));
    }
}

In the above code example, the strategy pattern is defined by defining a strategy interface (Strategy) and specifying it in the specific strategy class (OperationAdd and OperationSubtract) to implement the interface method. Different strategies are implemented by using the Context class.

2. Observer Pattern
The Observer Pattern defines a one-to-many dependency relationship, allowing multiple observer objects to monitor an observed object at the same time. When the observer object changes, all observer objects will be notified for corresponding processing.

Sample code:

// 定义被观察者接口
public interface Subject {
    void registerObserver(Observer observer);
    void removeObserver(Observer observer);
    void notifyObservers();
}

// 定义观察者接口
public interface Observer {
    void update(String message);
}

// 实现被观察者接口的具体被观察者类
import java.util.ArrayList;
import java.util.List;

public class ConcreteSubject implements Subject {
    private List<Observer> observers = new ArrayList<>();
    private String message;

    public void registerObserver(Observer observer) {
        observers.add(observer);
    }

    public void removeObserver(Observer observer) {
       observers.remove(observer);
    }

    public void notifyObservers() {
       for (Observer observer : observers) {
          observer.update(message);
       }
    }

    public void setMessage(String message) {
       this.message = message;
       notifyObservers();
    }
}

// 实现观察者接口的具体观察者类
public class ConcreteObserver implements Observer {
    private String name;

    public ConcreteObserver(String name) {
        this.name = name;
    }

    public void update(String message) {
       System.out.println(name + " received message: " + message);
    }
}

// 测试示例
public class ObserverPatternTest {
    public static void main(String[] args) {
       ConcreteSubject subject = new ConcreteSubject();

       ConcreteObserver observer1 = new ConcreteObserver("Observer 1");
       ConcreteObserver observer2 = new ConcreteObserver("Observer 2");
       ConcreteObserver observer3 = new ConcreteObserver("Observer 3");

       subject.registerObserver(observer1);
       subject.registerObserver(observer2);
       subject.registerObserver(observer3);

       subject.setMessage("Hello World!");
    }
}

In the above code example, the observer pattern defines an observed interface (Subject) and an observer interface (Observer ), and implement the interface methods in the specific observed class (ConcreteSubject) and observer class (ConcreteObserver). When the observed state changes, the observer is notified by calling the observer's interface method.

Conclusion:
This article introduces two common interface design patterns: strategy pattern and observer pattern, and provides specific Java code examples. These design patterns have extensive application value in software development, can improve the flexibility and scalability of code, and help us write better code.

Of course, in addition to the strategy pattern and the observer pattern, there are many other important interface design patterns in Java, which are worthy of our continued learning and exploration. By understanding and applying these interface design patterns, we can write code with better quality and maintainability.

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