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Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.
Enumeration is less safer than Iterator
Enumeration is fail safe whereas Iterator is fail fast
Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.
Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2
Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove
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Ans. Hibernate mapping configurations are used for mapping hibernate entities and corresponding DB Tables. Conventionally Entities and Table can share the same name and hence framework can provide implicit mapping instead of explicit mapping through configurations. Though it may result in little loss of flexibility in extreme cases but will work with all applications following the convention.
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Ans. Yes, It may result in some loss of flexibility as the application has to follow all conventions. Moreover it can contradict with other design paradigms or principles used in the application or framework.
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Ans. Convention over configuration is a way of software design used by frameworks that attempt to decrease the number of decisions that a developer is required to make without necessarily losing flexibility. The objective is to reduce the unnecessary configurations and follow conventions to accomplish that. For example - DB Entity and DB Table name conventionally should be same and hence shouldn't require configuring mapping between the two.
"Spring Boot" and "Ruby on Rails" have adopted this design principle.
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Q280. How can you extract integers from string values and add (sum it up) all the extracted integers? e.g "James34long4island322in3rdAvenue" ---> 34 4 322 3 = 363
Ans. synchronized is a keyword and a modifier. The synchronized keyword is used to indicate that a method can be accessed exclusively by one thread at a time.
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Ans. Frankly saying I dont see much use of method overloading as its just little design convenience as you can use the same name but still have binding to different methods depending on the need.
Method overriding is really important and is much more useful than method overloading. Along with other programming concepts like interfaces and dependency injection , it facilitates the development of software as libraries and plug-gable components.
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Ans. This looks like the case for optimistic locking wherein hibernate suspects that the information in table was updated by some other transaction after the entity was loaded by current transaction.
One way is to have synchronized entity state and don't detach the entity. Other could be to merge the entity with the table record rather than just directly persisting the entity.
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Ans. It's the way for synchronization wherein we can store version information in the table , so that if the same entity is updated by two transactions, the last to commit changes is informed of the conflict, and does not override the other transaction's work.
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Ans. Garbage collection mechanism frees up the memory that is no longer needed. In languages like C / C++ the deallocation needs to be done explicitly by the programmer and hence any leniency may result in memory leak. Garbage collection in java ensures that all unused memory is reclaimed and hence there are no memory leaks.Moreover it relieves the programmer from the hassle of carefully releasing all memory.
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Ans. Application is unable to insert a record as it violates a unique constraint.
The exception states the constraint and Table can be located by the Entity mapping. So I will go to the DB and will first check to which all columns the unique constraint applies. And then I will go and check the code and logs to see how come the duplicate column values were attempted to be inserted when they were not supposed to be.
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Ans. We can declare the reference as final to avoid reassignment but again we can always initialize the final reference to null. Even if there was any such facility available , it would have meant poor use of resources by assigning a new object in memory to each reference that's created. Many a times references are just meant to refer to other objects which already have a reference i.e sharing object by multiple references.
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Ans. I like to keep the names in Capital Camel case. Moreover I prefer to keep the names for classes, enums and interfaces such that they are easily distinguishable just by the pattern of their names.
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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. Likewise classes, methods also provide a way for code reuse and abstraction. Code is reused, clean and easy to understand if classified properly within classes and methods.
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Ans. Include directive includes the file at translation time (the phase of JSP life cycle where the JSP gets converted into the equivalent servlet) whereas the include action includes the file at runtime.
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