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Ans. Optional is a good way to protect application from runtime nullPointerException in case the the absent value has been represented as null. So basically Optional class provides the type checking during compile time and hence will never result in NPE.
Ans. Spring caching makes use of its intercepting capabilities to add caching to method calls. Therefore, the entire object is cached and reused. Hibernate, on the other hand, has more domain-specific knowledge of the Entity being cached and can handle the objects more appropriately.
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Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.
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Q400. Which of the following cannot be marked static ?
a. Constructors , Classes ( Outer ) , Classes ( nested ), Interfaces , Local variables , Inner Class methods and instance variables. b. Constructors , Classes ( Outer ) , Interfaces , Local variables , Class variables , Class Methods , Inner Class methods and instance variables. c. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables. d. Constructors , Classes ( Outer ) , Classes (Nested), Interfaces , Local variables , Inner Class methods and instance variables
Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.
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Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
Methods , Variables , Initialization Blocks and Outer Classes.
Methods , Variables , Initialization Blocks and nested Classes.
Which of the following cannot be marked static ?
Constructors , Classes ( Outer ) , Classes ( nested ), Interfaces , Local variables , Inner Class methods and instance variables.
Constructors , Classes ( Outer ) , Interfaces , Local variables , Class variables , Class Methods , Inner Class methods and instance variables.
Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.
Constructors , Classes ( Outer ) , Classes (Nested), Interfaces , Local variables , Inner Class methods and instance variables.
Q401. Interface can only have ...
a. Member elements and Methods. b. Static Variables and Static Methods. c. Static Final Variables and Instance Method Declarations. d. Member Elements , Instance Methods, Static variables and Static Methods.
Ans. Static Final Variables and Instance Method Declarations.
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Q403. If we try to add duplicate key to the HashMap, What will happen ?
a. It will throw an exception. b. It won't add the new Element without any exception. c. The new element will replace the existing element. d. Compiler will identify the problem and will throw an error.
Ans. The new element will replace the existing element.
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Ans. It will result in compilation error as primitive char cannot be casted to Integer object, alternatively we can cast it to primitive int like following
System.out.println((int)'a');
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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. Deprecated annotation is for documentation purpose only. It doesn't enforce anything but would mark the method name as crossed to signify that the client should refrain from using it.
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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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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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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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