Design Patterns Differences Interview Questions

By | April 24, 2023

In Java, how does the Chain of Responsibility pattern differ from the Decorator pattern?

The Chain of Responsibility pattern and the Decorator pattern is both structural design patterns in Java that involve wrapping objects, but they have different intents and implementations.

The Chain of Responsibility pattern is used to handle requests in a chain of objects, where each object in the chain has the ability to handle the request or pass it on to the next object in the chain. It involves decoupling the sender of a request from its receiver, allowing multiple objects to have the chance to handle the request. The Chain of Responsibility pattern typically involves a handler interface or class, concrete handler classes that implement the handler interface and either handle the request or pass it on to the next handler in the chain, and a client that sends requests to the first handler in the chain.

The Decorator pattern, on the other hand, is used to dynamically add functionality to an object by wrapping it with one or more decorators. It involves adding behavior to an object without changing its interface, allowing different combinations of behavior to be applied to the object. The Decorator pattern typically involves a component interface or class, concrete component classes that implement the component interface and provide the base functionality, and concrete decorator classes that wrap the component and add additional behavior.

In summary, the main difference between the Chain of Responsibility pattern and the Decorator pattern in Java is that the Chain of Responsibility pattern is used to handle requests in a chain of objects, while the Decorator pattern is used to dynamically add functionality to an object by wrapping it with one or more decorators.

How does the Template Method pattern differ from the Strategy pattern in Java?

The Template Method pattern and the Strategy pattern are both behavioral patterns in Java that involve encapsulating behavior, but they have different intents and implementations.

The Template Method pattern is used to define the skeleton of an algorithm in a superclass, allowing subclasses to provide concrete implementations of specific steps in the algorithm. It involves defining a template method in a superclass that calls abstract or concrete methods that can be overridden by subclasses to provide specific implementations. The Template Method pattern typically involves an abstract class that defines the template method and abstract or concrete methods that are called by the template method, and concrete subclasses that provide the specific implementations of the abstract or concrete methods.

The Strategy pattern, on the other hand, is used to encapsulate interchangeable behaviors and select them at runtime. It involves decoupling an algorithm from the client that uses it, allowing different algorithms to be selected based on the context. The Strategy pattern typically involves a strategy interface or class, concrete strategy classes that implement the strategy interface and encapsulate different algorithms, and a context class that uses the strategy to perform a task.

In summary, the main difference between the Template Method pattern and the Strategy pattern in Java is that the Template Method pattern is used to define the skeleton of an algorithm in a superclass, allowing subclasses to provide concrete implementations of specific steps in the algorithm, while the Strategy pattern is used to encapsulate interchangeable behaviors and select them at runtime based on the context.

Can you describe the differences between the Visitor pattern and the Iterator pattern in Java?

The Visitor pattern and the Iterator pattern are both behavioral patterns in Java that involve traversing collections of objects, but they have different intents and implementations.

The Visitor pattern is used to separate an algorithm from an object structure on which it operates, allowing new operations to be added without modifying the object structure. It involves defining an interface or abstract class for the visitor and implementing the visitor to operate on the elements of the object structure. The Visitor pattern typically involves an object structure that provides an interface to accept visitors, a visitor interface or abstract class that defines the visit methods for the elements of the object structure, and concrete visitor classes that implement the visitor interface or abstract class and provide the specific behavior for the visit methods.

The Iterator pattern, on the other hand, is used to traverse a collection of objects without exposing its implementation details. It involves defining an iterator interface or abstract class that provides methods to access the elements of the collection and a concrete iterator class that implements the iterator interface or abstract class and provides the specific implementation for the methods. The Iterator pattern typically involves a collection interface or abstract class that provides a method to create iterators for the collection and a concrete collection class that implements the collection interface or abstract class and provides the specific implementation for the createIterator method.

In summary, the main difference between the Visitor pattern and the Iterator pattern in Java is that the Visitor pattern is used to separate an algorithm from an object structure on which it operates, while the Iterator pattern is used to traverse a collection of objects without exposing its implementation details.

In Java, what distinguishes the Singleton pattern from the Prototype pattern?

The Singleton pattern and the Prototype pattern are both creational design patterns in Java that involve creating objects, but they have different intents and implementations.

The Singleton pattern is used to ensure that a class has only one instance and provide a global point of access to it. It involves creating a class that has a private constructor and a static method to access the single instance of the class. The Singleton pattern typically involves a private constructor, a static variable that holds the single instance of the class, and a static method that provides access to the single instance.

The Prototype pattern, on the other hand, is used to create new objects by cloning existing objects, rather than by creating new instances from scratch. It involves creating a prototype object and cloning it to create new instances. The Prototype pattern typically involves a prototype interface or abstract class that defines a clone method, a concrete prototype class that implements the prototype interface or abstract class and provides a concrete implementation of the clone method, and a client that uses the prototype to create new instances.

In summary, the main difference between the Singleton pattern and the Prototype pattern in Java is that the Singleton pattern is used to ensure that a class has only one instance and provide a global point of access to it, while the Prototype pattern is used to create new objects by cloning existing objects, rather than by creating new instances from scratch.

How does the Abstract Factory pattern differ from the Bridge pattern in Java?

The Abstract Factory pattern and the Bridge pattern are both design patterns in Java that involve decoupling abstractions from their implementations, but they have different intents and implementations.

The Abstract Factory pattern is used to provide an interface for creating families of related or dependent objects without specifying their concrete classes. It involves defining an abstract factory interface or class that declares methods for creating abstract products, concrete factory classes that implement the abstract factory interface or class and create concrete products, and abstract product interfaces or classes that declare methods for the products.

The Bridge pattern, on the other hand, is used to decouple an abstraction from its implementation so that the two can vary independently. It involves defining an abstraction interface or class that defines the operations to be performed and a bridge interface or class that defines the operations to be implemented. The Bridge pattern typically involves an abstraction interface or class that holds a reference to the bridge interface or class, concrete abstraction classes that implement the abstraction interface or class and delegate the implementation to the bridge, and concrete bridge classes that implement the bridge interface or class and provide the specific implementation for the operations.

In summary, the main difference between the Abstract Factory pattern and the Bridge pattern in Java is that the Abstract Factory pattern is used to provide an interface for creating families of related or dependent objects without specifying their concrete classes, while the Bridge pattern is used to decouple an abstraction from its implementation so that the two can vary independently.

Can you explain the differences between the Builder pattern and the Factory Method pattern in Java?

The Builder pattern and the Factory Method pattern are both creational design patterns in Java that involve creating objects, but they have different intents and implementations.

The Factory Method pattern is used to provide an interface for creating objects, but allows subclasses to decide which class to instantiate. It involves defining a factory method in an abstract class or interface that returns an object of a subclass. The Factory Method pattern typically involves a creator class that declares the factory method, concrete creator classes that implement the factory method to create concrete objects, and product classes that define the objects created by the factory method.

The Builder pattern, on the other hand, is used to separate the construction of a complex object from its representation, allowing the same construction process to create different representations. It involves defining a builder interface or class that declares methods for building the parts of the object and a director class that controls the construction process. The Builder pattern typically involves a builder interface or class that defines the methods for building the parts of the object, concrete builder classes that implement the builder interface or class to construct different representations of the object, and a director class that uses the builder to construct the final object.

In summary, the main difference between the Factory Method pattern and the Builder pattern in Java is that the Factory Method pattern is used to provide an interface for creating objects, but allows subclasses to decide which class to instantiate, while the Builder pattern is used to separate the construction of a complex object from its representation, allowing the same construction process to create different representations.

How does the Flyweight pattern differ from the Proxy pattern in Java?

The Flyweight pattern and the Proxy pattern are both design patterns in Java that involve optimizing object creation and usage, but they have different intents and implementations.

The Flyweight pattern is used to minimize memory usage by sharing common state between multiple objects. It involves creating a flyweight factory that maintains a pool of flyweight objects and a flyweight interface or class that defines the intrinsic state of the flyweight objects. The Flyweight pattern typically involves client objects that use the flyweight factory to create or retrieve flyweight objects and a context object that defines the extrinsic state of the flyweight objects.

The Proxy pattern, on the other hand, is used to provide a surrogate or placeholder for another object to control its access or add additional functionality. It involves creating a proxy object that has the same interface as the real object and forwards requests to the real object, but may also perform additional actions before or after the request. The Proxy pattern typically involves a subject interface or class that defines the common interface for the proxy and the real object, a real subject class that implements the subject interface or class and provides the actual behavior, and a proxy class that also implements the subject interface or class and forwards requests to the real subject, but may also perform additional actions.

In summary, the main difference between the Flyweight pattern and the Proxy pattern in Java is that the Flyweight pattern is used to minimize memory usage by sharing common state between multiple objects, while the Proxy pattern is used to provide a surrogate or placeholder for another object to control its access or add additional functionality.

Can you describe the differences between the Mediator pattern and the Observer pattern in Java?

The Mediator pattern and the Observer pattern are both behavioral design patterns in Java that involve communication between objects, but they have different intents and implementations.

The Observer pattern is used to establish a one-to-many dependency between objects, where a change in one object triggers updates in all dependent objects. It involves defining a subject interface or class that maintains a list of observers and provides methods for adding, removing, and notifying observers. The Observer pattern typically involves concrete observer classes that implement the observer interface and register with the subject to receive notifications, and a concrete subject class that maintains the list of observers and notifies them when its state changes.

The Mediator pattern, on the other hand, is used to define an object that encapsulates the communication between a set of objects, decoupling them from each other. It involves defining a mediator interface or class that defines the methods for communicating with the objects and a concrete mediator class that implements the mediator interface or class and manages the communication between the objects. The Mediator pattern typically involves colleague interfaces or classes that define the methods for interacting with the mediator and a concrete colleague class that implements the colleague interface or class and communicates with the mediator.

In summary, the main difference between the Mediator pattern and the Observer pattern in Java is that the Observer pattern is used to establish a one-to-many dependency between objects, where a change in one object triggers updates in all dependent objects, while the Mediator pattern is used to define an object that encapsulates the communication between a set of objects, decoupling them from each other.

In Java, what distinguishes the Composite pattern from the Decorator pattern?

The Composite pattern and the Decorator pattern are both structural design patterns in Java that involve composing objects, but they have different intents and implementations.

The Composite pattern is used to represent a hierarchical structure of objects as a tree, where each object in the tree can be treated uniformly. It involves defining a component interface or class that defines the methods for accessing and manipulating the components of the tree, and a composite class that implements the component interface or class and contains a list of child components. The Composite pattern typically involves leaf classes that represent the individual objects in the tree and composite classes that represent the nodes in the tree.

The Decorator pattern, on the other hand, is used to add functionality to an existing object dynamically, without changing its interface. It involves defining a component interface or class that defines the methods for the object’s basic functionality, and a decorator class that implements the component interface or class and adds additional behavior to the object. The Decorator pattern typically involves concrete component classes that represent the basic objects, and concrete decorator classes that wrap the basic objects and add additional functionality.

In summary, the main difference between the Composite pattern and the Decorator pattern in Java is that the Composite pattern is used to represent a hierarchical structure of objects as a tree, where each object in the tree can be treated uniformly, while the Decorator pattern is used to add functionality to an existing object dynamically, without changing its interface.

How does the Chain of Responsibility pattern differ from the Mediator pattern in Java?

The Chain of Responsibility pattern and the Mediator pattern are both behavioral design patterns in Java that involve communication between objects, but they have different intents and implementations.

The Chain of Responsibility pattern is used to handle a request or task by a series of objects, each of which can handle the request or pass it to the next object in the chain. It involves defining a handler interface or class that defines the methods for handling the request, and a chain of handler objects that implement the handler interface or class and handle the request in sequence. The Chain of Responsibility pattern typically involves concrete handler classes that check if they can handle the request and either handle it or pass it to the next handler in the chain.

The Mediator pattern, on the other hand, is used to define an object that encapsulates the communication between a set of objects, decoupling them from each other. It involves defining a mediator interface or class that defines the methods for communicating with the objects, and a concrete mediator class that implements the mediator interface or class and manages the communication between the objects. The Mediator pattern typically involves colleague interfaces or classes that define the methods for interacting with the mediator and a concrete colleague class that implements the colleague interface or class and communicates with the mediator.

In summary, the main difference between the Chain of Responsibility pattern and the Mediator pattern in Java is that the Chain of Responsibility pattern is used to handle a request or task by a series of objects, each of which can handle the request or pass it to the next object in the chain, while the Mediator pattern is used to define an object that encapsulates the communication between a set of objects, decoupling them from each other.

Can you explain the differences between the Adapter pattern and the Proxy pattern in Java?

The Adapter pattern and the Proxy pattern are both structural design patterns in Java that involve wrapping an object, but they have different intents and implementations.

The Adapter pattern is used to adapt the interface of an existing object to meet the requirements of a new client. It involves defining a target interface or class that represents the requirements of the client, and an adapter class that implements the target interface or class and wraps an existing object with an incompatible interface, translating calls to the target interface or class to calls to the wrapped object’s interface. The Adapter pattern typically involves adapting an object’s interface by either class inheritance or object composition.

The Proxy pattern, on the other hand, is used to control access to an object, by providing a surrogate or placeholder for the object that can be used to perform additional tasks such as logging, security, or caching. It involves defining a subject interface or class that defines the methods for accessing the object, and a proxy class that implements the subject interface or class and wraps the real object, providing additional behavior such as access control or caching. The Proxy pattern typically involves creating a proxy object that controls access to the real object by either holding a reference to the real object or by creating the real object on demand.

In summary, the main difference between the Adapter pattern and the Proxy pattern in Java is that the Adapter pattern is used to adapt the interface of an existing object to meet the requirements of a new client, while the Proxy pattern is used to control access to an object, by providing a surrogate or placeholder for the object that can be used to perform additional tasks such as logging, security, or caching.

In Java, what distinguishes the Facade pattern from the Composite pattern?

The Facade pattern and the Composite pattern are both structural design patterns in Java that involve simplifying the complexity of a system, but they have different intents and implementations.

The Facade pattern is used to provide a simple interface to a complex system, by encapsulating its components behind a unified interface. It involves defining a facade class that provides a simplified interface to a set of complex subsystem classes, hiding their implementation details from the client. The Facade pattern typically involves composing the complex subsystem objects together to provide a unified interface to the client.

The Composite pattern, on the other hand, is used to represent a hierarchical structure of objects as a tree, allowing clients to treat individual objects and groups of objects uniformly. It involves defining a component interface or class that defines the common methods for accessing and manipulating the objects in the tree, and two concrete classes, one representing leaf objects and the other representing composite objects that contain other components. The Composite pattern typically involves composing the leaf and composite objects together to create a tree-like structure.

In summary, the main difference between the Facade pattern and the Composite pattern in Java is that the Facade pattern is used to provide a simple interface to a complex system by encapsulating its components behind a unified interface, while the Composite pattern is used to represent a hierarchical structure of objects as a tree, allowing clients to treat individual objects and groups of objects uniformly.

How does the Visitor pattern differ from the Interpreter pattern in Java?

The Visitor pattern and the Interpreter pattern are both behavioral design patterns in Java that involve manipulating a collection of objects, but they have different intents and implementations.

The Visitor pattern is used to separate the algorithm from the object structure on which it operates, by allowing new operations to be added to the object structure without modifying the objects themselves. It involves defining a visitor interface or class that declares a set of methods, each of which corresponds to a different type of object in the structure, and a set of concrete visitor classes that implement the visitor interface or class and provide the behavior for each method. The Visitor pattern typically involves accepting a visitor object into each object in the structure, which calls back the appropriate method on the visitor to perform the desired operation.

The Interpreter pattern, on the other hand, is used to interpret a language or grammar by defining a set of rules and using them to parse and evaluate input expressions. It involves defining an abstract expression interface or class that declares a method for interpreting an expression, and a set of concrete expression classes that implement the expression interface or class and represent the different elements of the language or grammar. The Interpreter pattern typically involves constructing a parse tree of expression objects from the input expression, and then recursively evaluating each node of the tree to produce a result.

In summary, the main difference between the Visitor pattern and the Interpreter pattern in Java is that the Visitor pattern is used to separate the algorithm from the object structure on which it operates, by allowing new operations to be added to the object structure without modifying the objects themselves, while the Interpreter pattern is used to interpret a language or grammar by defining a set of rules and using them to parse and evaluate input expressions.

In Java, what distinguishes the Strategy pattern from the Template Method pattern?

The Strategy pattern and the Template Method pattern are both behavioral design patterns in Java that involve defining a family of algorithms, but they have different intents and implementations.

The Strategy pattern is used to encapsulate a family of related algorithms and make them interchangeable, by defining a common interface for all the algorithms and allowing them to be selected at runtime. It involves defining a strategy interface or class that declares a method for performing the algorithm, and a set of concrete strategy classes that implement the strategy interface or class and provide the different variations of the algorithm. The Strategy pattern typically involves passing a strategy object to a context object, which delegates the algorithm to the strategy object.

The Template Method pattern, on the other hand, is used to define the skeleton of an algorithm in a base class, but allow its specific steps to be defined in subclasses, by defining a set of abstract methods that the subclasses must implement. It involves defining an abstract template class that declares a method for the algorithm and a set of abstract methods that represent the specific steps of the algorithm, and a set of concrete classes that inherit from the template class and implement the abstract methods. The Template Method pattern typically involves calling the template method on the template object, which calls the abstract methods to perform the specific steps of the algorithm.

In summary, the main difference between the Strategy pattern and the Template Method pattern in Java is that the Strategy pattern is used to encapsulate a family of related algorithms and make them interchangeable, by defining a common interface for all the algorithms and allowing them to be selected at runtime, while the Template Method pattern is used to define the skeleton of an algorithm in a base class, but allow its specific steps to be defined in subclasses, by defining a set of abstract methods that the subclasses must implement.

How does the Bridge pattern differ from the Abstract Factory pattern in Java?

The Bridge pattern and the Abstract Factory pattern are both creational design patterns in Java that involve decoupling an abstraction from its implementation, but they have different intents and implementations.

The Bridge pattern is used to separate an abstraction from its implementation so that they can be developed and modified independently. It involves defining an abstraction interface or class that declares a set of operations, and a separate implementation interface or class that provides the implementation details for the operations. The Bridge pattern typically involves creating a bridge object that contains a reference to the abstraction object and the implementation object, and uses them to delegate the operations.

The Abstract Factory pattern, on the other hand, is used to create families of related objects without specifying their concrete classes, by defining a factory interface or class that declares a set of methods for creating the objects, and a set of concrete factory classes that implement the factory interface or class and provide the different variations of the objects. The Abstract Factory pattern typically involves creating an abstract factory object that contains a reference to a concrete factory object, and using it to create the objects.

In summary, the main difference between the Bridge pattern and the Abstract Factory pattern in Java is that the Bridge pattern is used to separate an abstraction from its implementation so that they can be developed and modified independently, while the Abstract Factory pattern is used to create families of related objects without specifying their concrete classes. The Bridge pattern involves creating a bridge object that contains a reference to the abstraction object and the implementation object, and uses them to delegate the operations, while the Abstract Factory pattern involves creating an abstract factory object that contains a reference to a concrete factory object, and using it to create the objects.

In Java, what distinguishes the Strategy pattern from the State pattern?

How does the Builder pattern differ from the Abstract Factory pattern in Java?

What distinguishes the Facade pattern from the Adapter pattern in Java?

 

Can you explain the difference between the Observer pattern and the Pub/Sub pattern in Java?

What are the main differences between the Command pattern and the Strategy pattern in Java?

That’s all about Design pattern differences.

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