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Ans. It's a feature to lazily initialize dependencies , relationship and associations from the Database. Any related references marked as @OneToMany or @ManyToMany are loaded lazily i.e when they are accessed and not when the parent is loaded.
Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.
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Ans. Its a method which cannot be overridden. Compiler throws an error if we try to override a method which has been declared final in the parent class.
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Ans. ACID stands for Atomicity, Consistency, Isolation, Durability is a set of properties of database transactions.
Atomicity means all or nothing. i.e parts of a transaction shouldn't commit if any one of them fails. Either the whole transaction should succeed or it should be complete rollback.
Consistency means that any transaction should lead database from one stabe state to another.
Isolation means that the execution of transaction results in a system state that would be obtained if transactions were executed serially.
Durability means that when a transaction is committed it forms the permanent state of database.
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Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.
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Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy.
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Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems.
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Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.
Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count
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Q19. What was the driving force to introduce default methods in Interfaces wef from Java 8 ?
Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs.
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Ans. The finally keyword is used to create a block of code that follows a try block. A finally block of code always executes, whether or not an exception has occurred.
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Ans. In case we specify them explicitly we can have control over constraint name as otherwise they will be system generated. It provides an ease in case we plan to drop the constraint in future.
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