Design Patterns

The Singleton Design Pattern ensures that a class has only one instance and provides a global point of access to it. To achieve thread safety, reflection safety, and serialization safety, you need to handle specific concerns. Let’s explore how to implement a Singleton pattern that addresses these concerns. Key Concepts: Thread Safety: Ensures that the Singleton instance is created in a thread-safe manner, so multiple threads do not create multiple instances. Reflection Safety: Ensures that the Singleton instance cannot be created using reflection, which can bypass the singleton restriction. Serialization Safety: Ensures that the Singleton instance remains a single instance even after deserialization. Implementation Here’s a Singleton implementation that addresses these concerns: ...

The Prototype Design Pattern is a creational pattern that involves creating new objects by copying an existing object, known as the prototype. This pattern is useful when the cost of creating a new object is more expensive than copying an existing one. It allows you to create objects without specifying their exact class and provides a way to clone objects efficiently. Components of the Prototype Design Pattern: Prototype: An interface or abstract class that declares a clone() method for copying itself. ConcretePrototype: Implements the Prototype interface and provides the implementation for the clone() method. Client: Uses the clone() method to create new instances of objects. Simple Example: Let’s create a simple example where we have a Shape interface with a clone() method. We will implement concrete prototypes like Circle and Rectangle that can be cloned. ...

The Factory Design Pattern is a creational pattern that provides a way to create objects without specifying the exact class of the object that will be created. It defines an interface for creating an object, but allows subclasses to alter the type of objects that will be created. Components of the Factory Design Pattern: Product: The interface or abstract class that defines the type of object to be created. ConcreteProduct: Implements the Product interface and defines the specific object to be created. Creator: The interface or abstract class that declares the factory method for creating Product objects. ConcreteCreator: Implements the Creator interface and overrides the factory method to return an instance of ConcreteProduct. Simple Example: Let’s create a simple example where we have a Vehicle interface, and concrete implementations like Car and Bike. We will use a factory to create instances of these vehicles. ...

The Builder Design Pattern is a creational pattern that provides a way to construct complex objects step by step. It separates the construction of a complex object from its representation, allowing the same construction process to create different representations. Components of the Builder Design Pattern: Builder: An abstract class or interface that defines the steps for creating parts of a complex object. ConcreteBuilder: Implements the Builder interface to construct and assemble parts of the product. Product: The complex object being built. Director: Constructs an object using the Builder interface. It defines the order in which to execute the building steps. Example 1: Let’s create a simple example where we build a Computer object with various components like CPU, RAM, and storage. We will use the Builder Pattern to construct the Computer object step by step. ...

The Abstract Factory Design Pattern is a creational pattern that provides an interface for creating families of related or dependent objects without specifying their concrete classes. It involves creating an abstract factory interface that defines methods for creating abstract products, and concrete factories that implement this interface to create specific families of products. Components of the Abstract Factory Design Pattern: AbstractFactory: Declares methods for creating abstract product objects. ConcreteFactory: Implements the AbstractFactory interface to create specific products. AbstractProduct: Declares an interface for a type of product object. ConcreteProduct: Implements the AbstractProduct interface. Client: Uses the AbstractFactory to get instances of AbstractProduct. Simple Example: Let’s create a simple example where we have two types of products: Chair and Sofa. We will have two families of products: Modern and Victorian. The Abstract Factory will create the appropriate family of products. ...

The Proxy Design Pattern is a structural pattern that provides a surrogate or placeholder for another object. It allows you to control access to the real object, providing additional functionality such as access control, lazy initialization, or logging. The proxy pattern involves creating a proxy class that implements the same interface as the real object and delegates requests to the real object. Components of the Proxy Design Pattern: Subject: An interface or abstract class that defines the common interface for both the RealSubject and the Proxy. RealSubject: The actual class that performs the real operations. Proxy: A class that implements the Subject interface and maintains a reference to the RealSubject. It controls access to the RealSubject and can add additional behavior. Simple Example: Let’s create a simple example where we use a Proxy to control access to a RealImage object. The RealImage class represents a large image that we want to load and display, but we’ll use a Proxy to manage access and load the image only when necessary. ...

The Flyweight Design Pattern is a structural pattern that optimizes memory usage by sharing common parts of objects to support a large number of similar objects efficiently. This pattern is used when you have a large number of objects with shared states and you want to minimize memory usage. Components of the Flyweight Design Pattern: Flyweight: An interface or abstract class that declares methods for managing and accessing extrinsic state. ConcreteFlyweight: Implements the Flyweight interface and defines the intrinsic state of the object. The intrinsic state is shared across all instances of the flyweight. FlyweightFactory: Manages the creation and reuse of Flyweight objects. It ensures that flyweights are shared properly. Client: Maintains references to flyweights and uses them. Simple Example: Let’s create a simple example where we manage a collection of Character objects in a text editor. Each character may have different formatting (e.g., bold or italic), but the characters themselves (e.g., ‘A’, ‘B’, ‘C’) are shared. ...

The Facade Design Pattern is a structural pattern that provides a simplified interface to a complex subsystem. It hides the complexity of the subsystem and makes it easier to use. The pattern involves creating a facade class that delegates requests to the appropriate components of the subsystem. Components of the Facade Design Pattern: Facade: The class that provides a simplified interface to the complex subsystem. Subsystem Classes: The classes that make up the complex subsystem. They handle the actual operations and functionality. Simple Example: Let’s create a simple example where we have a home theater system with several components. We will use the Facade Pattern to provide a simplified interface for turning on and off the home theater system. ...

The Decorator Design Pattern is a structural pattern that allows you to dynamically add behavior to an object without altering its structure. This pattern provides a flexible alternative to subclassing for extending functionality. Components of the Decorator Design Pattern: Component: The interface or abstract class defining the common interface for both the core object and decorators. ConcreteComponent: The class implementing the Component interface. This is the core object to which additional behaviors can be added. Decorator: An abstract class or interface that implements the Component interface and contains a reference to a Component object. It delegates operations to the Component and can add additional behavior. ConcreteDecorator: A class extending the Decorator that adds specific behavior. Simple Example: Let’s create a simple example where we have a Coffee class that can be decorated with various add-ons like milk and sugar. ...

The Composite Design Pattern is a structural pattern that allows you to compose objects into tree-like structures to represent part-whole hierarchies. This pattern treats both individual objects and compositions of objects uniformly. It’s useful when you need to work with hierarchies of objects and want to treat single objects and compositions of objects in a consistent way. Components of the Composite Design Pattern: Component: The abstract base class or interface that declares the common interface for both leaf and composite objects. Leaf: The concrete class that represents individual objects in the composition. It implements the component interface. Composite: The concrete class that represents compositions of leaf objects. It implements the component interface and contains child components. Simple Example: Let’s use a file system example where we have File and Directory components. A Directory can contain multiple File or Directory objects, and we want to be able to treat both File and Directory objects uniformly. ...