Briefly talk about the creative structural and behavioral design patterns in Java. In which Java source code classes can these design patterns be seen?
Design patterns are standard solutions to common problems in software design. They can be categorized into three main types: creational, structural, and behavioral patterns. Here’s a brief overview of each category, along with examples of where they can be found in Java:
Creational design patterns deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. They help in controlling the instantiation process.
Common Creational Patterns:
Singleton: Ensures a class has only one instance and provides a global point of access to it.
java.lang.Runtime is a classic example of the Singleton pattern.Factory Method: Defines an interface for creating an object but lets subclasses alter the type of objects that will be created.
java.util.Calendar class uses a factory method to create instances of different calendar types.Abstract Factory: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
javax.xml.parsers.DocumentBuilderFactory class is an example of the Abstract Factory pattern.Structural design patterns deal with object composition, helping to ensure that if one part of a system changes, the entire system doesn’t need to do the same.
Common Structural Patterns:
Adapter: Allows incompatible interfaces to work together. It acts as a bridge between two incompatible interfaces.
java.util.Arrays class has methods that adapt arrays to the List interface.Decorator: Adds new functionality to an object dynamically without altering its structure.
java.io.BufferedReader class decorates the Reader class to add buffering capabilities.Facade: Provides a simplified interface to a complex subsystem.
javax.swing.JOptionPane class provides a simple interface for dialog boxes.Behavioral design patterns focus on communication between objects, defining how objects interact and communicate with one another.
Common Behavioral Patterns:
Observer: Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
java.util.Observer and java.util.Observable classes implement the Observer pattern.Strategy: Defines a family of algorithms, encapsulates each one, and makes them interchangeable. The strategy lets the algorithm vary independently from clients that use it.
java.util.Comparator interface allows different comparison strategies for sorting.Command: Encapsulates a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations.
java.awt.event.ActionListener interface can be seen as a Command pattern where actions are encapsulated.These design patterns are widely used in Java and can be found in various standard libraries and frameworks. Understanding these patterns can significantly improve code maintainability, scalability, and readability.