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Q631. How can one determine if JVM is 32-bit or 64-bit from Java Program ?

Ans. There is a Java system property "sun.arch.data.model" that can tell if JVM is 32 bit of 64 bit

System.getProperty("sun.arch.data.model") can be used to get that property.

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Q632. What is coupling and Cohesion ?

Design

Ans. Coupling is the degree of interdependence between software modules, a measure of how closely connected two modules are or the strength of the relationships between modules.

Cohesion refers to the degree to which the elements of a module belong together. Cohesion measures the strength of relationship between pieces of functionality within a given module.

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Usually asked with Questions related to Generics.

Q633. What are Type Erasures in Java ?

Core Java

Ans. Type erasure applies to the use of generics. When generics are used, they're pre compiled into compile time checks and execution-time casts.

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Q634. Have you ever felt the need of keeping the constructor private ?

Design

Ans. Yes, When either we don't want an object to be created ( class having all static elements and hence not required ) or object to be created using a static method or static block. One such example could be a situation when we would like app to load objects at start up and we would like to restrict new object creation by any request.

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Q635. How do you prefer to store money values in your application ?

Core Java

Ans. At Application level we use either Double or BigDecimal , preferably BigDecimal. At Database level we use Number with decimal precision 3.

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Q636. What is Dirty read in Database Transactions ?

Database

Ans. A dirty read occurs when a transaction is allowed to read data from a row that has been modified by another running transaction but not yet committed.

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Q637. What does the web status code 404,500 and 200 mean ?

Java EE

Ans. 404 means the resource is not found on the server.The resource might not be deployed correctly.

500 means internal server error which means that resource was located but then it resulted in some exception or error.

200 means Ok.

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Q638. Write an SQL Statement to add a foreign key constraint in oracle ?

Database

Ans. ALTER TABLE <Table_Name> ADD CONSTRAINT <Constraint_Name> FOREIGN KEY (<Column_Name>) REFERENCES <Foreign_Table>(<Foreign_Column>);

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Basic and Very Frequently asked.

Q639. What is Polymorphism in Java ?

Core Java

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

Sample Code for overloading

Sample Code for overriding

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Frequently asked to fresh graduates.

Q640. What is ACID ?

Database

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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Frequently asked Design Pattern interview question.

Q641. What is a prototype design pattern ?

Design

Ans. The prototype pattern is a creational design pattern. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects. Prototype is used when we need duplicate copies of objects.

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Q642. How to Bulk upload the data into Oracle database?

Database

Ans. We can use external table feature of Oracle.

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Q643. Can you assign value to a static final type at runtime ?

Core Java

Ans. No

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Q644. In case of a synchronized method, Does the method only gets locked or the whole object ?

Core Java

Ans. Just the method gets locked.

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Q645. There is a Table Student having Student Id, Name and Total Marks. Can you please write an SQL that will display the maximum marks obtained by a student ?

Database

Ans. SELECT MARKS FROM STUDENT ORDER BY MARKS DESC LIMIT 1;

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Q646. How to count total number of tables in database ?

Database

Ans. SELECT COUNT(*) FROM information_schema.tables

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Q647. Have you heard about the external table feature of Oracle ?

Database

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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Q648. Can we have try statement without catch? If try statement contains return will the finally block be executed? What happens if there is an exception inside finally block?

Core Java

Ans. Yes, with finally.

Yes, finally block will be executed even if there is no exception in try block.

If finally throws an exception, the exception gets thrown to the calling module.

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Q649. What is a Database Trigger ?

Database

Ans. A trigger is a special kind of stored procedure that automatically gets executed upon an event in the database server.

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Q650. What is a Database sequence ?

Database

Ans. Its a feature wherein database creates unique values incremental values to be stored as primary key for the table.

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Q651. What is a Database Procedure ?

Database

Ans. Stored procedures are a batch of SQL statements along with programming constructs ( if else, loops etc ) and stored as a single program that can be called by different clients and hence reused.

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Frequently asked to Fresh graduates.

Q652. Write a program to implement Binary search ?

Core Java

Ans. http://algs4.cs.princeton.edu/11model/BinarySearch.java.html

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Q653. What is the use of Combiners ?

BigData

Ans. Combiners are used to increase the efficiency of a Map Reduce program. They are used to aggregate intermediate map output locally on individual mapper outputs. Combiners can help you reduce the amount of data that needs to be transferred across to the reducers.

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Q654. Can you narrate some sample usage for Bigdata ?

BigData

Ans. One common usage is predictive analytic using huge current or past data. For example - Using recent medical data ( diagnosis and procedure ), one can identify the pattern of diseases or the procedures that has to eventually applied upon certain diagnosis. This analysis might help in predicting the diseases that might occur to a patient. the other usage could be to identify the future spending patterns of the population by analyzing the past and current habits.

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Q655. What is Hadoop Framework ?

BigData

Ans. Hadoop is an open source framework , written in java by apche software foundation. This framework is used to write applications to process vast amount of data. Processing happens in parallel on large clusters which could have 1000 of computers. It processes data in a very reliable and fault tolerant manner.

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Q656. What are the two main components of Hadoop System ?

BigData

Ans. Distributed file system and Map Reduce system.

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Q657. How to tackle duplicate classes in maven build ?

Maven

Ans. The simplest way is to ignore them if Maven enforcer plugin is complaining about it but it may lead to runtime problems later.

We can do the dependency:tree to see from where these duplicate ones are coming and hence can exclude the duplicate one.

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Q658. Have you heard of Ban Duplicate Classes Maven enforcer plugin ? What is its use ?

Maven

Ans. Yes , we have been using this plugin with our projects and its purpose is to warn and stop the Build if there are duplicates of the same package and class are being carried either directly or through transitive dependencies. the duplicate could be coming through different types of dependencies or through different versions of the same dependency. Its purpose is to make sure that there is only one copy thats being used at compile time and runtime and hence shouldnt later result in runtime problems.

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Q659. What are the advantages and disadvantages of Factory Design Pattern ?

Design

Ans. Object Oriented Design Patterns is the science of identifying the pattern to make objects communicate in a way to effectively implement a Solution.

Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object. So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

Advantage of Factory Pattern - Loose Coupling and Segregation of Responsibilities. Now instead of hard binding the complete logic to decide the nature and shape of the object on the basis of some conditions, you are assigning the responsibility to some other object and hence making the relationship loosely coupled and hence main tenable.

Disadvantages - Before Understanding the Dis-advantages , we should understand that these patterns were chosen after a period of evolution and research and almost best fit for the required solution, otherwise these patterns would have easily been replaced by now.

Though the advantages of these pattern surpass the disadvantages keeping in mind the decreasing cost of resources and increasing scale of applications, but still loose coupling by means of additional objects results in decreased performance.

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Q660. What are the benefits of Enums ?

Core Java

Ans. Enums in Java are used to declare predefined objects and then reuse them. they offer many benefits

1. Enum instance are type safe and thread safe.

2. Enum instances are singleton and hence reused.

3. If we use Enums with Switch , It makes sure that the passed argument is either of its instance and hence provides a safeguard.

4. If we use Enum with Sorted Collections we can sort the elements with a predefined priorities ( as per constant declaration in enum )

5. We can use Enum as a Factory by defining its constructor.

6. We can store related constant data within enum. For example - If we know the values for the map upfront, we can alternatively use an enum.

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