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Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime. | ||||
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Ans. In first case, there would be 2 DB calls in worst case and 1 in best case. In 2nd approach there will be always 2 DB calls. Decision on the approach should depend on the following considerations - 1. How costly is the call to DB ? Are we using indices , hibernate etc If calls to DB are costly , 1st approach should be the choice. 2. Exception Book keeping load upon exception. The benefit of saving 1st call in approach 1 should be bigger than the Book keeping for the exception. 3. Probability of the exception in first apparoach. If the DB Table is almost empty, it makes sense to follow Approach 1 as majority of the 1st calls will pass through without exception. | ||||
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Like Discuss Correct / Improve  database   insert-update   db exceution plan   db strategy   design   architecture   technical lead | ||||
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Ans. It could be worthy to move a method to util class if the method needs to be shared, doesn't require polymorphic behavior and need not be overridden in special cases. Don't belong to one group through is-a relationship ( You can share through parent class method ) Don't implement a specific interface ( java 8 default methods ) Doesn't involve complex computing as you will be loosing the benefit of object state with just static method. Doesn't require polymorphic behavior as static methods don't participate in runtime polymorphism. | ||||
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Like Discuss Correct / Improve  utility classes   util classes   static methods   application design   rare | ||||
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Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules. Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module. | ||||
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Like Discuss Correct / Improve  coupling  cohesion Asked in 10 Companies   frequent | ||||
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This question was recently asked at 'Myntra'.This question is still unanswered. Can you please provide an answer. | ||||
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Ans. Central place for configuring dependencies. No need to create object, container manage all this By using Run time polymorphism and association. Facilities development of framework / libraries by injecting implementation classes in the implementation code. | ||||
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Like Discuss Correct / Improve  dependency injection  IOC  inversion of control | ||||
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Ans. Each has it's own advantages Batching requires less resources but may result in loosing whole batch in case of failure whereas concurrency even though is little more expensive in terms of resources but would result in minimal loss in case of failure. In case messages are to be consumed in a particular order, batching them in that order and then consuming them makes better sense. if incoming messages are not continuous , it makes more sense to do concurrency as we need not wait for all messages to form a batch and flush. Though time sensitivity can be added but that would add unnecessary complexity. | ||||
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Ans. Subject has state, it keeps a list of observers. On the other hand, an Observable is really just a function that sets up observation. While Subjects are Observables, Subjects also implement an Observer interface. | ||||
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Ans. 1. Design patterns are abstraction heavy and hence sometimes creates memory and performance overheads. 2. Sometimes they create unnecessary complexity without much added advantage. | ||||
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Ans. Adapter. | ||||
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Ans. Adapter object has a different input than the real subject whereas Proxy object has the same input as the real subject. Proxy object is such that it should be placed as it is in place of the real subject. | ||||
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Ans. The Difference between these patterns in only the intent. Adapter is used because the objects in current form cannot communicate where as in Facade , though the objects can communicate , A Facade object is placed between the client and subject to simplify the interface. | ||||
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Ans. Exception Handling Throw mechanism. | ||||
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Ans. Listeners. | ||||
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Ans. Setter injection Constructor injection Interface injection Look-up method/method injection | ||||
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Ans. In First Case , Lock for the synchronized block will be received only if singleton == null whereas in second case every thread will acquire the lock before executing the code. The problem of synchronization with singleton will only happen when the object has not be instantiated. Once instantiated , the check singleton == null will always generate true and the same object will be returned and hence no problem. First condition will make sure that synchronized access ( acquiring locks ) will only take place if the object has not been created so far. | ||||
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Like Discuss Correct / Improve  java   singleton   synchronization | ||||
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Ans. Both are creational design patterns. Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted. In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects. | ||||
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Ans. Object Oriented Design Patterns is the science of identifying the pattern to make objects communicate in a way to effectively implement a Solution. Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object. So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object. Advantage of Factory Pattern - Loose Coupling and Segregation of Responsibilities. Now instead of hard binding the complete logic to decide the nature and shape of the object on the basis of some conditions, you are assigning the responsibility to some other object and hence making the relationship loosely coupled and hence main tenable. Disadvantages - Before Understanding the Dis-advantages , we should understand that these patterns were chosen after a period of evolution and research and almost best fit for the required solution, otherwise these patterns would have easily been replaced by now. Though the advantages of these pattern surpass the disadvantages keeping in mind the decreasing cost of resources and increasing scale of applications, but still loose coupling by means of additional objects results in decreased performance. | ||||
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Like Discuss Correct / Improve  factory design pattern  design pattern | ||||
Very Frequently asked to Senior Software Engineers or Developers. | ||||
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Ans. [Open Ended Answer] | ||||
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Like Discuss Correct / Improve  design patterns Asked in 17 Companies intermediate   frequent | ||||
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This question was recently asked at 'Booking.com,InterContinental Hotels,Caissa,Workday'.This question is still unanswered. Can you please provide an answer. | ||||
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Ans. Encapsulation and Polymorphism. We need methods to access variables in a polymorphic way as overriding only happens with methods and not with variables. Moreover getter provides a way to minimally open the access window for the object and hence provides better encapsulation. To add to those, we can have validation in the getter method before returning elements. | ||||
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Ans. Authentication / Authorization URL forwarding Auditing / Logging Localization | ||||
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Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user. | ||||
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Ans. Observable is emiting data and Observer is subscribing to catch the data | ||||
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This question was recently asked at 'Aloha Technologies'.This question is still unanswered. Can you please provide an answer. | ||||
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Ans. For Cloning-exception,For deserialization-read.resolve() | ||||
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Ans. Deserialization. In serialization, we can save the object of a byte stream into a file or send over a network. Suppose if you serialize the Singleton class, and then again de-serialize that object, it will create a new instance, hence deserialization will break the Singleton pattern. To overcome this issue, we need to override readResolve() method in the Singleton class and return the same Singleton instance. | ||||
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Ans. I would choose Eager as the cost for 1 additional object is too minute for any such consideration. Eager Loading results in Faster access ( Object available at load time) at the cost of additional space. Lazy loading results in space saving ( Object available at first use ) at the cost of access speed. | ||||
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Ans. Strategy deals only with decision making at runtime so Interfaces should be used. | ||||
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Ans. In GUI programming, an object that can be registered to be notified when events of some given type occur. The object is said to listener? for the events. | ||||
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