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Q361. What is the main difference between unique key and primary key ?

Ans. Primary key will not accept NULL values whereas Unique key can accept one NULL value.

A table can have only primary key whereas there can be multiple unique key on a table.

A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.

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Q362. What is the difference between Subject and Observable ?

Angular

^{This question is still unanswered. Can you please provide an answer.}

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Q363. What does pipe does on an observable ?

RxJs

Ans. With pipe we specify the operator function to which this observable is passed for transforming the observable.

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Q364. Why do we do transformation on the observable itself rather than doing it in the subscriber ?

RxJs

Ans. Because that way we just need to do that transformation at one place and not within each subscriber. Single source of truth.

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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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