What are the commonly used design patterns in java frameworks?

Necessary Java framework design patterns: Singleton pattern: ensures that a class is instantiated only once and provides a global access point. Factory Pattern: Responsible for creating objects, allowing the use of different types of objects without changing the code. Strategy pattern: Defines a family of algorithms and allows selection of specific algorithms. Decorator Pattern: Dynamically extends object functionality without modifying the original object. Proxy pattern: Provide an object to act as a proxy for another object, controlling access to the original object or enhancing its functionality.

Essential design patterns in the Java framework

The design pattern is a proven, universal, reusable code structure. They provide elegant and maintainable solutions to common programming problems. In a Java framework, a deep understanding of these patterns is crucial. Here are some of the most common patterns:

1. Singleton pattern:
Ensure that a class is instantiated only once. This pattern simplifies resource management and consistency by providing a global access point.

public class Singleton {
    private static Singleton instance;
 
    private Singleton() {
        // Private constructor to prevent external instantiation
    }
 
    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

2. Factory pattern:
Responsible for creating objects without specifying their specific classes. It allows applications to use different types of objects without changing the code.

public interface ShapeFactory {
    Shape createShape(String type);
}

public class CircleFactory implements ShapeFactory {
    @Override
    public Shape createShape(String type) {
        if (type.equals("CIRCLE")) {
            return new Circle();
        } else {
            return null;
        }
    }
}

3. Strategy mode:
Define a series of algorithms and allow the client to select a specific algorithm without affecting other code. It provides a loosely coupled, configurable way to handle different behaviors.

public interface PaymentStrategy {
    void pay(double amount);
}

public class CreditCardPaymentStrategy implements PaymentStrategy {
    @Override
    public void pay(double amount) {
        // Process credit card payment
    }
}

4. Decorator pattern:
Dynamically add additional responsibilities to the object. It allows extending the functionality of the original object without modifying it.

public class Shape {
    protected String color;
 
    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }
}

public class DecoratorShape extends Shape {
    protected Shape decoratedShape;
 
    public DecoratorShape(Shape decoratedShape) {
        this.decoratedShape = decoratedShape;
    }

    @Override
    public String getColor() {
        return decoratedShape.getColor();
    }
}

5. Proxy pattern:
Provide an object to act as a proxy for another object. It can be used to control access to the original object or enhance its functionality.

public class Service {
    public void doSomething() {
        // Perform some service
    }
}

public class ServiceProxy implements Service {
    private Service service;
 
    public ServiceProxy(Service service) {
        this.service = service;
    }

    @Override
    public void doSomething() {
        // Perform additional logic
        service.doSomething();
        // Perform additional logic
    }
}

These are just a few design patterns commonly used in Java frameworks. Mastering these patterns is critical to building maintainable, scalable, and efficient applications.

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