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Q1981. Explain Generics in Java ?

Ans. Generics are a facility of generic programming that were added to the Java programming language in 2004 within J2SE5.0. They allow "a type or method to operate on objects of various types while providing compile-time type safety.

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Q1982. What is ORM or Object Relationship Mapping ?

Ans. ORM is the mapping technique, which maps object with relational data model. As we know that in java we need objects we can not user data in relational(in table form). So ORM is set of guideline which allows us to map relational data model in object form.

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Q1983. What are the uses of Abstraction ?

Ans. Loose Coupling
Facilitates designing complex applications by making them modular.

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Q1984. What are the disadvantages of Bean Auto Wiring in Spring ?

Ans. It can always be overridden with explicit wiring. Moreover it's confusing if we use both explicit as well as explicit wiring in the project.

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Q1985. How can we track of all objects created in an application ?

Ans. We can store the references in a collection by adding to those objects in the collection. We can create a class "ObjectRegistry" with a collection or multiple collections with a search algorithm to look for the already collected objects.

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Q1986. Why is JVM called Virtual machine ?

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Q1987. Lets say we have a set "set1" with objects of Class A, Class has a non static string called element1, Write a code ( using lambda expression ) to see if there is any object in the set with element1 = "Hello".

Ans. set1.stream().filter(p->p.element1.equals("Hello")).findAny().isPreent();

or

set1.stream().map(A::getElement1).anyMatch("Hello"::equals)

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Q1988. Which of the OOP's features facilitate dependency injection ?

Ans. Inheritance , Runtime Polymorphism and Composition.

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Q1989. Is Runtime Polymorphism possible without Inheritance ?

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q1990. Is dependency injection possible if we don't have inheritance / Composition ?

Ans. Without composition - No, as it's the core of dependency injection.

With Inheritance - Yes, through interface implementation.

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Q1991. Why is Java such an important Programming language ?

Ans. Because of following features

Object Oriented and hence helps build maintainable and easily enhanceable code.
Platform Independence and hence can be executed anywhere
Fast due to JIT compiler

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Q1992. Why Java is considered more purer object oriented language than C++ ?

Ans. Because of

lack of use of pointers,
Lack of structural programming and
Lack of Multiple Inheritance

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Q1993. Does Wrapper classes produces immutable objects ?

Ans. Yes

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Q1994. Why shouldn't we use string concatenation extensively or in a loop ?

Ans. Because String being an immutable object creates a new object upon each concatenation cycle. If there is any such need , we should use String Builder whose objects are mutable.

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Q1995. What do we mean by a Data Type ?

Ans. if you have similar type of data or objects or entities, then we can give them a type with unique name. And this name will be our Data type.

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Q1996. As root, if you have to assign the owner for the file and set only read permission for the owner, Write a unix command to do it.

Ans. chmod 477

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Q1997. In the following code, which text will get printed immediately after Hello

for(int countx=0;countx<10;count++){
System.out.println("World");
for(int countx=0;countx<10;count++){
System.out.println("Friend");
for(int countx=0;countx<10;count++){
System.out.println("Hello");
break;
}
System.out.println("Buddy");
}
}

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Q1998. Which of the two - iteration or recursion - is slower ?

Ans. Any function call is slower than the code in the same method as Java has to maintain stack of meta and function call information. So recursion is slower.

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Q1999. In case of generic class declared like following , What can T hold

class MyClass<T>{
T element;
}

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Q2000. If we have to specify a collection of a particular information like List of addresses, How can we represent that in a JSON ?

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Q2001. Which type of testing involves use of mocking frameworks ?

Ans. Unit Testing

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Q2002. Can and Should we mock calls in integration tests ?

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Q2003. What features would you like to see in Java 10 ?

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Q2004. Can we instantiate the object of derived class if parent constructor is private ?

Ans. No

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Q2005. How do you design microservices?

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Q2006. Can an enum extend another enum ?

Ans. No

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Q2007. Can we have a sub enum within an enum ?

Ans. Yes

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Q2008. Write a SQL to remove records with a duplicate field in a Table ?

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Q2009. How can we make sure that we don't receive duplicate messages from the Kafka Topic ?

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Q2010. If a Map needs to be accessed simultaneously by multiple threads, which collection class should be used ?

Ans. ConcurrentHashMap

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