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Q961. What is cascade ?

Ans. Instead of Saving Parent as well as Child Entities individually , Hibernate provides the option to persist / delete the related entities when the Parent is persisted.

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Q962. What are the different Cascade types ?

Hibernate

Ans. Detach, Merge , Persist , Remove , Refresh

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Q963. Which type of associated Entities are Eagerly loaded by Default ?

Hibernate

Ans. OneToOne

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Q964. After which Hibernate version , related Entities are initialized lazily ?

Hibernate

Ans. After Hibernate 3.0

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Q965. Can we declare Entity class as final ?

Hibernate

Ans. Yes but as Hibernate creates the Proxy Classes inherited from the Entity Classes to communicate with Database for lazy initialization. Declaring entity classes as final will prohibit communication with database lazily and hence will be a performance hit.

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Q966. What are the restrictions for the entity classes ?

Hibernate

Ans. 1. Entity classes should have default constructor.

2. Entity classes should be declared non final.

3. All elements to be persisted should be declared private and should have public getters and setters in the Java Bean style.

4. All classes should have an ID that maps to Primary Key for the table.

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Q967. What is the difference between int[] x; and int x[]; ?

Core Java

Ans. No Difference. Both are the acceptable ways to declare an array.

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Q968. What are the annotations used in Junit with Junit4 ?

Ans. @Test

The Test annotation indicates that the public void method to which it is attached can be run as a test case.

@Before

The Before annotation indicates that this method must be executed before each test in the class, so as to execute some preconditions necessary for the test.

@BeforeClass

The BeforeClass annotation indicates that the static method to which is attached must be executed once and before all tests in the class.

@After

The After annotation indicates that this method gets executed after execution of each test.

@AfterClass

The AfterClass annotation can be used when a method needs to be executed after executing all the tests in a JUnit Test Case class so as to clean-up the set-up.

@Ignores

The Ignore annotation can be used when you want temporarily disable the execution of a specific test.

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Frequently asked these days as there are major changes in Java 8.

Q969. What are new features introduced with Java 8 ?

Core Java

Ans. Lambda Expressions , Interface Default and Static Methods , Method Reference , Parameters Name , Optional , Streams, Concurrency.

Sample Code for Lambda

Sample Code for interface default

Sample Code for Optional

Sample Code for Streams

Sample Code for java.time

Sample Code for Predicate

Sample Code for Consumer

Sample Code for MapMerge

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Q970. Does java allow implementation of multiple interfaces having Default methods with Same name and Signature ?

Core Java

Ans. No. Compilation error.

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Q971. What are Default Methods ?

Core Java

Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method.

Sample Code for interface default

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Q972. Can we use static method definitions in Interfaces ?

Core Java

Ans. Yes, Effective Java 8.

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Q973. Can we access Interface static method using Interface references ?

Ans. No, only using Interface Name.

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Q974. Can we have default method with same name and signature in the derived Interface as the static method in base Interface and vice versa ?

Ans. Yes , we can do that as static methods are not accessible using references and hence cannot lead to conflict. We cannot do inverse as Default methods cannot be overridden with the static methods in derived interface.

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Frequently asked at Manhattan Associates ( Based on 2 feedback )

Q975. What is a Lambda Expression ? What's its use ?

Core Java

Ans. Its an anonymous method without any declaration.

Lambda Expression are useful to write shorthand Code and hence saves the effort of writing lengthy Code.

It promotes Developer productivity, Better Readable and Reliable code.

Sample Code for lambda

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Try 1 Question(s) Test

Q976. Difference between Predicate, Supplier and Consumer ?

Core Java

Ans. Predicate represents an anonymous function that accepts one argument and produces a result.

Supplier represents an anonymous function that accepts no argument and produces a result.

Consumer represents an anonymous function that accepts an argument and produces no result.

Sample Code for Predicate

Sample Code for Supplier

Sample Code for Consumer

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Q977. What is the difference between namenode and datanode in Hadoop?

BigData

Ans. NameNode stores MetaData (No of Blocks, On Which Rack which DataNode is stored etc) whereas the DataNode stores the actual Data.

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Q978. Write a program to see if the number is perfect number or not ?

Core Java

Ans. http://www.c4learn.com/c-programs/program-to-check-whether-number-is.html

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Q979. Difference between a Pointer and a Reference ?

Ans. We can't get the address of a reference like a pointer. Moreover we cannot perform pointer arithmetic with references.

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Q980. Difference between TCP and UDP ?

Networking

Ans. http://www.cyberciti.biz/faq/key-differences-between-tcp-and-udp-protocols/

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Q981. What things you would care about to improve the performance of Application if its identified that its DB communication that needs to be improved ?

Solution

Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements )

2. Restructuring Indexes.

3. DB Caching Tuning ( if using ORM )

4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM )

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Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)

Q982. Explain Singleton Design Pattern ?

Design

Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html

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Q983. Can we override compareTo method for Enumerations ?

Core Java

Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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Q984. How to create a Junit to make sure that the tested method throws an exception ?

Ans. Using annotation Test with the argument as expected exception.

@Test (expected = Exception.class)

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Q985. Write an SQL to find all records having all upper case alphanumeric characters in a field ?

Ans. Select * from Table where field = upper(field)

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Q986. Write an SQL to find all records having all numeric characters in a field ?

Ans. Select * from Table where isnumeric(field) = 1;

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Q987. If you are given a choice to implement the code to either Insert a Record or Update if already exist, Which approach will you follow ?

1. Insert into the DB Table. If exception occurs, update the existing record.
2. Check if the record exists and update it if it exists, If not insert a new record.

Solution

Ans. In first case, there would be 2 DB calls in worst case and 1 in best case. In 2nd approach there will be always 2 DB calls.

Decision on the approach should depend on the following considerations -

1. How costly is the call to DB ? Are we using indices , hibernate etc

If calls to DB are costly , 1st approach should be the choice.

2. Exception Book keeping load upon exception.

The benefit of saving 1st call in approach 1 should be bigger than the Book keeping for the exception.

3. Probability of the exception in first apparoach.

If the DB Table is almost empty, it makes sense to follow Approach 1 as majority of the 1st calls will pass through without exception.

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Q988. What will the following code do ?

String dateStr = "2011 11 19";
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
Date date = dateFormat.parse(dateStr);
System.out.println(date);

Ans. It will throw the ParseException as the date format doesn't abide with the format of the specified date.

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Q989. Can we extend an Enum ?

Core Java

Ans. No. Enums are final by design.

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Q990. What are the considerations to be made in case of loops in Java ?

Core Java

Ans. 1. It shouldn't result in infinite loop. Please make sure that you have a condition that will terminate the loop and that condition should be reached.

2. Make sure to use the break statement if you aspire to only look for something. Not using break will unnecessarily execute it till the end of for loop in some cases.

3. Similarly use continue to execute the loop with next iteration and bypass the rest of the code block if required.

4. Try to avoid multiple nesting of for loops. If it''s required, Make sure to use break and continue properly so as to avoid some unnecessary processing.

5. Make sure to use try catch within the loop and not outside the for loop if you expect it to continue if one of the iteration fails.

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