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Q361. Why can't we declare a class abstract as well as final ?

Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.

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Q362. In the following code , how many methods needs to be implemented in Class B ?

public interface A{
   public void method1();
   public void method2();
   public void method3();
}

abstract class B implements A{
}

Core Java

Ans. As Class B has been declared abstract , we can either implement any of these methods and just declare rest of them abstract.

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Q363. What is unmodifiable set / unmodifiable map ? How can we create one ?

Ans. It is an unmodifiable / read only view of the underlying collection. We can use

Collections.unmodifiableSet(Set set)
Collections.unmodifiableMap(Map map)
Collections.unmodifiableCollection(Collection collection)

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Q364. What should a class do if its extending an abstract class ?

Core Java

Ans. It should either implement the abstract methods or re-declare them abstract.

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Q365. Which method needs to be implemented if a class is implementing comparable interface ?

Core Java

a. comp

b. compare

c. compareTo

d. compareEquals

Ans.c. compareTo

Q366. What is Dirty Read in Database Transactions ?

Database

a. Data Read by Transaction 2 which hasn't yet updated by Transaction 1

b. Data Read by Transaction 2 which has been updated and commited by Transaction 1

c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

d. Inability of Transaction 2 to read Data when Transaction 1 is updating.

Ans.c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

Q367. Which of the following is not true for abstract classes ? Reference

Core Java

a. Abstract Class is only meant to be sub classed and not supposed to be instantiated.

b. Abstract class handlers can be used to handle derived class objects.

c. We can't have an abstract class without abstract methods.

d. Abstract class has member elements.

Ans.c. We can't have an abstract class without abstract methods.

Q368. Which of the following class creates immutable objects ? Reference

Core Java

a. String

b. StringBuffer

c. StringBuilder

d. None of these create immutable objects.

Ans.a. String

Q369. Which of the following can be declared abstract ?

Core Java

a. static methods

b. instance methods

c. static variable

d. instance variables

Ans.b. instance methods

Q370. In majority of the cases, the following join will give maximum number of results ? Reference

Database

a. Inner Join

b. Outer Join

c. Left Join

d. Right Join

Ans.b. Outer Join

Q371. Which if the following is true for SQL Joins ? Reference

Database

a. Left Join and Right Join gives equal number of Results

b. Outer Join and Inner Join gives equal number of Results

c. Inner Join gives maximum number of results records

d. Inner Join gives minimum number of result records

Ans.d. Inner Join gives minimum number of result records

Q372. Which of the following is not true for Prepared Statements ?

Database

a. Prepared Statements provides better performance

b. Prepared Statements prevent SQL Injection attacks

c. Prepared Statements provide ORM capabilities

d. Prepared Statement provides DB side caching

Ans.c. Prepared Statements provide ORM capabilities

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