Java design patterns are essential for solving common problems in software design. Here are some advanced patterns you should explore:

1. Strategy Pattern 🔄

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It's useful for dynamic behavior switching.

public interface Strategy {
    void algorithmInterface();
}

public class ConcreteStrategyA implements Strategy {
    public void algorithmInterface() {
        System.out.println("Using Strategy A");
    }
}

public class Context {
    private Strategy strategy;
    
    public Context(Strategy strategy) {
        this.strategy = strategy;
    }
    
    public void executeStrategy() {
        strategy.algorithmInterface();
    }
}
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2. Observer Pattern 📢

This pattern allows an object to notify other objects about changes in its state. Ideal for event handling systems.

public interface Observer {
    void update(String message);
}

public class Subject {
    private List<Observer> observers = new ArrayList<>();
    
    public void addObserver(Observer observer) {
        observers.add(observer);
    }
    
    public void notifyObservers(String event) {
        observers.forEach(obs -> obs.update(event));
    }
}

3. Visitor Pattern 🧭

The Visitor pattern decouples data structure hierarchies from operations. It's great for adding new operations without modifying existing classes.

public interface Visitor {
    void visit(ElementA element);
    void visit(ElementB element);
}

public class ConcreteVisitor implements Visitor {
    public void visit(ElementA element) {
        System.out.println("Visited ElementA");
    }
    
    public void visit(ElementB element) {
        System.out.println("Visited ElementB");
    }
}

4. Template Method Pattern 🧱

This pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. It's commonly used in frameworks.

public abstract class TemplateClass {
    public final void templateMethod() {
        primitiveOperation1();
        primitiveOperation2();
    }
    
    protected abstract void primitiveOperation1();
    protected abstract void primitiveOperation2();
}

5. Proxy Pattern 🌐

Proxies provide a surrogate or placeholder for another object to control access to it. Often used for lazy loading or access control.

public class ProxyClass implements TargetInterface {
    private RealSubject realSubject;
    
    public void request() {
        if (realSubject == null) {
            realSubject = new RealSubject();
        }
        realSubject.request();
    }
}

For more examples, check out our Java Design Patterns Introduction tutorial. 🚀

observer_pattern