diff --git a/faq.md b/faq.md deleted file mode 100644 index 107ee1e68..000000000 --- a/faq.md +++ /dev/null @@ -1,88 +0,0 @@ ---- -layout: page -link-title: FAQ -title: FAQ - Java Design Patterns -description: Java Design Pattern FAQ answers the most commonly asked design patterns questions. -permalink: /faq/ -icon: fa-question -page-index: 5 ---- - -### Q1: What is the difference between State and Strategy patterns? {#Q1} - -While the implementation is similar they solve different problems. The State -pattern deals with what state an object is in - it encapsulates state-dependent -behavior. -The Strategy pattern deals with how an object performs a certain task - it -encapsulates an algorithm. - -### Q2: What is the difference between Strategy and Template Method patterns? {#Q2} - -In Template Method the algorithm is chosen at compile time via inheritance. -With Strategy pattern the algorithm is chosen at runtime via composition. - -### Q3: What is the difference between Proxy and Decorator patterns? {#Q3} - -The difference is the intent of the patterns. While Proxy controls access to -the object Decorator is used to add responsibilities to the object. - -### Q4: What is the difference between Chain of Responsibility and Intercepting Filter patterns? {#Q4} - -While the implementations look similar there are differences. The Chain of -Responsibility forms a chain of request processors and the processors are then -executed one by one until the correct processor is found. In Intercepting -Filter the chain is constructed from filters and the whole chain is always -executed. - -### Q5: What is the difference between Visitor and Double Dispatch patterns? {#Q5} - -The Visitor pattern is a means of adding a new operation to existing classes. -Double dispatch is a means of dispatching function calls with respect to two -polymorphic types, rather than a single polymorphic type, which is what -languages like C++ and Java _do not_ support directly. - -### Q6: What are the differences between Flyweight and Object Pool patterns? {#Q6} - -They differ in the way they are used. - -Pooled objects can simultaneously be used by a single "client" only. For that, -a pooled object must be checked out from the pool, then it can be used by a -client, and then the client must return the object back to the pool. Multiple -instances of identical objects may exist, up to the maximal capacity of the -pool. - -In contrast, a Flyweight object is singleton, and it can be used simultaneously -by multiple clients. - -As for concurrent access, pooled objects can be mutable and they usually don't -need to be thread safe, as typically, only one thread is going to use a -specific instance at the same time. Flyweight must either be immutable (the -best option), or implement thread safety. - -As for performance and scalability, pools can become bottlenecks, if all the -pooled objects are in use and more clients need them, threads will become -blocked waiting for available object from the pool. This is not the case with -Flyweight. - -### Q7: What are the differences between FluentInterface and Builder patterns? {#Q7} - -Fluent interfaces are sometimes confused with the Builder pattern, because they share method chaining and a fluent usage. However, fluent interfaces are not primarily used to create shared (mutable) objects, but to configure complex objects without having to respecify the target object on every property change. - -### Q8: What is the difference between java.io.Serialization and Memento pattern? {#Q8} - -Memento is typically used to implement rollback/save-point support. Example we might want to mark the state of an object at a point in time, do some work and then decide to rollback to the previous state. - -On the other hand serialization may be used as a tool to save the state of an object into byte[] and preserving the contents in memory or disk. When someone invokes the memento to revert object's previous state then we can deserialize the information stored and recreate previous state. - -So Memento is a pattern and serialization is a tool that can be used to implement this pattern. Other ways to implement the pattern can be to clone the contents of the object and keep track of those clones. - - -### Q9: What's the difference between “API Gateway” and “Aggregator Microservices”? Isn't it the same? {#Q9} - -The API Gateway : Aggregate calls to microservices in a single location. The user makes a single call to the API Gateway, and the API Gateway then calls each relevant microservice. -Use the API Gateway pattern when you're also using the Microservices pattern and need a single point of aggregation for your microservice calls. - -Aggregator Microservices : The user makes a single call to the Aggregator, and the aggregator then calls each relevant microservice and collects the data, apply business logic to it, and further publish is as a REST Endpoint.Use the Aggregator Microservices pattern when you need a unified API for various microservices, regardless the client device. - - -