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Q391. What are collection types in Hibernate ?

Hibernate

Ans. Bag, Set , List , Array, Map

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Very frequently asked if being interviewed for hibernate. Frequently asked in Tata Consultancy (TCS) and Overstock.com

Q392. Difference between load and get ?

Hibernate

Ans. If id doesnt exist in the DB load throws an exception whereas get returns null in that case.get makes the call to DB immediately whereas load makes the call to proxy.

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Q393. What is the way to rollback transaction if something goes wrong using hibernate API ?

Hibernate

Ans. We can have the code calling Hibernate API within try block and can have transaction.rollback within Catch.

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Q394. 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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Q395. 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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Q396. 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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Q397. Can we use static method definitions in Interfaces ?

Core Java

Ans. Yes, Effective Java 8.

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Q398. 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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Q399. Where do we configure repositories in Maven ?

Maven

Ans. Within settings.xml in either MAVEN_HOME or .M2 directory.

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Q400. What are different type of repositories in Maven ?

Maven

Ans. Local and Remote.

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Q401. How does Maven looks for a resource ?

Maven

Ans. It refers to the settings.xml to look for the repositories to look for the resource. First It looks into the configured local repository, then it looks into the configured Remote repositories. If the resource is still not found , it looks it within maven repository central i.e repo1.maven.org. If its still not found, it throws the exception saying "Unable to find resource in repository central".

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Q402. What is repository central ?

Maven

Ans. Its the repository provided by Maven. In case your POM specify the dependencies and its not available in the configured local and the remote repository. It then looks for the resource in Maven Central. Maven provides most of the generic dependency resources at this remote location.

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Q403. 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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Q404. How can we test methods individually which are not visible or declared private ?

Ans. We can either increase their visibility and mark them with annotation @VisibleForTesting or can use reflection to individually test those methods.

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Q405. When does an application throw NullPointerException ?

Core Java

Ans. When it tries to access an object element or method using reference which is actually null.

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Q406. What are the steps to be performed while coding Junit with Mocking framework ?

JUnit

Ans. Initialize required objects for working with mocks and tested method
Set the mock behaviour on dependent objects
Execute the tested method
Perform assertions
Verify if a method is invoked or not

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Q407. Name few Dependency Injection frameworks ?

Ans. Google Guice , Spring , PicoContainer and Dagger.

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Q408. What will be the output of this code ?

Set mySet = new HashSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
for(String s: mySet){
System.out.println(s);
}

Ans. It will print 4567,5678 and 6789 but Order cannot be predicted.

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Q409. What will be the output of this code ?

Set mySet = new HashSet();
mySet.add("4567");
mySet.add("5678");
mySet.add("6789");
System.out.println(s.get(0));

Ans. This will give compile time error as we cannot retrieve the element from a specified index using Set. Set doesn't maintain elements in any order.

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Q410. What will be the output of the following code ?

enum Day {
MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY
}

public class BuggyBread1{
public static void main (String args[]) {
Set mySet = new TreeSet();
mySet.add(Day.SATURDAY);
mySet.add(Day.WEDNESDAY);
mySet.add(Day.FRIDAY);
mySet.add(Day.WEDNESDAY);
for(Day d: mySet){
System.out.println(d);
}
}
}

Core Java

Ans. WEDNESDAY
FRIDAY
SATURDAY

Only one FRIDAY will be printed as Set doesn't allow duplicates.Elements will be printed in the order in which constants are declared in the Enum. TreeSet maintains the elements in the ascending order which is identified by the defined compareTo method. compareTo method in Enum has been defined such that the constant declared later are greater than the constants declared prior.

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Q411. How to generate getters and setters automatically in eclipse ?

Eclipse

Ans. Right Click -> Source -> Generate Getters and Setters.

and it will open up a dialog wherein we can select the fields to generate Getters and Setters.

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Q412. 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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Q413. Why can't we use this in static context ?

Core Java

Ans. Static methods can be called using instance references wherein this would have made sense but static method can also be called using Class name wherein this would mean nothing and hence forbidden.

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Q414. How is Abstraction implemented in Java ?

Core Java

Ans. Abstraction is provided in Java by following ways -

Coding to the ( Interfaces / Abstract Classes ) or contracts

By Encapsulating details within classes and exposing the minimal Door ( few public methods )

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Q415. What are some different logging levels for log4j ?

Log4j

Ans. DEBUG
ERROR
ALL
WARN
INFO
FATAL
OFF
TRACE
TRACE_INT
WARN

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Not frequently asked as it was introduced with Java 8.

Q416. What is the use of Optional ?

Core Java

Ans. Optional is a good way to protect application from runtime nullPointerException in case the the absent value has been represented as null. So basically Optional class provides the type checking during compile time and hence will never result in NPE.

For ex -

List> intList = new ArrayList>();
intList.add(Optional.empty());
intList.add(Optional.of(new Employee("abc")));
intList.add(Optional.of(new Employee("xyz")));
intList.add(Optional.of(new Employee("123")));
System.out.println(intList.get(0).getName());

So Now , even when the first list element is empty, this code will never throw an NullPointerException.

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Q417. Can we generate Java Documentation using Export -> JavaDoc using a jar file ?

Eclipse

Ans. Yes, If the jar contains the source code. No, If it contains only classes.

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Rarely asked as it was introduced with Java 8.

Q418. Name few "Optional" classes introduced with Java 8 ?

Core Java

Ans. http://www.buggybread.com/2015/01/java-optional-classes-and-interfaces.html

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Q419. Name few IO Stream classes and interfaces ?

Core Java

Ans. http://www.buggybread.com/2015/01/java-stream-io-classes-and-interfaces.html

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Q420. Name few File IO related classes and interfaces ?

Core Java

Ans. http://www.buggybread.com/2015/01/java-file-io-classes-and-interfaces.html

Sample Code for File

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