Interview Questions and Answers for 'Io' | Search Interview Question

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Q391. Difference beween HashSet and TreeSet ?

Ans. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type )

2. TreeSet doesnt allow null elements whereas HashMap does.

3. As TreeSet orders elements and is hence insertion is comparatively slower.

4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time.

5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally.

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Q392. Which is better in terms of performance - Iterator or Spliterator ?

Core Java

Ans. Spliterator has better performance potential than iterators but only if the potential is used. Spliterator can iterate streams in parallel as well as in sequence whereas iterator can only iterate in sequence.

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Q393. What is Java NumberFormatException ?

Core Java

Ans. NumberFormatException is the exception that Java throws when we try to convert one data type to the Number data type but the value is not parsable to be a Number.

For example , the following code will result in the NumberFormatException

String string = "Buggy";
int strtoInt = Integer.parseInt(string);

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Q394. How can you check if a String is a 10 digit number by using regular expression ?

Core Java

Ans. We can use \d{10} as the expression to check that

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Q395. How can we catch an exception thrown by another thread ?

Core Java

Ans. http://stackoverflow.com/a/6548203/2789764

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Q396. 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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Q397. 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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Basic and Very Frequently asked.

Q398. 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.

Q399. 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.

Q400. 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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Frequently asked.

Q401. When does the finally block gets executed ?

Core Java

Ans. A finally block of code always executes, whether or not an exception has occurred.The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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Q402. What is the difference between Collections.emptyList() and creating new instance of List using new ?

Core Java

Ans. But Collections.emptyList() returns an Immutable list whereas new arraylist() creates a mutable list.

Advantage of getting an empty list using Collections.emptyList is that it returns a singleton list which can be shared among many references and hence made immutable. This is good fit for situations where we would like to initialize a list to basic minimum empty to avoid null pointer exception.

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Q403. 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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Q404. 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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Q405. 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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Q406. Explain Exception Hierarchy in Java SE ?

Core Java

Ans. <a href="http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/" rel="nofollow">http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/</a>

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Q407. Which data structure would you recommend for ordered and sorted data?

Core Java

Ans. TreeSet and TreeMap are used for maintaining sorted elements.

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Q408. What is the difference between URI, URL and URN ?

Java EE

Ans. URI stands for Uniform Resource Indicator
URL stands for Uniform Resource Locator
URN stands for Uniform Resource Name

URI = URL + URN

For ex - http://javasearch.buggybread.com/InterviewQuestions/questionSearch.php?keyword=url

This is URI. The string from start till .php is URL whereas keyword=url is URN.

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Q409. Which is the root interface of Collection classes in Java ?

Core Java

Ans. java.util.Collection

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Q410. What happens to the Exception object after the exception handling is done ?

Core Java

Ans. As with all other objects its garbage collected after its usage unless its rethrown.

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Q411. Why Collection interface does not extend Cloneable interface ?

Core Java

Ans. Here is the list of classes that implements Collections Interface - http://www.buggybread.com/2015/02/java-collections-classes-that-implement.html

Having Collection interface to extend Cloneable interface would mean necessarily implement clone method by all implementing classes. As not all collection classes allow duplicate elements, it makes no sense to clone elements for them.

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Q412. What is meant by size and index of a collection ?

Core Java

Ans. As the name suggest size is the size of collection / data structure i.e number of elements or memory utilized by the collection.

Index is the position of an element in a collection or data structure.

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Q413. How and when the Buffer is cleared when using Buffered Writer Classes ?

Core Java

Ans. Buffer is cleared in 2 circumstances, i.e 1. naturally when the buffer is filled and 2. explicitly when the method flush is called ( for flushing the residual )

Ideally we just need to call flush once at the end of file writing so that the residual content should be dumped to file.

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Q414. What is IdentityHashMap ?

Core Java

Ans. IdentityHashMap is a class that implements AbstractMap and provides a data structure with Elements having Key Value pair, just like HashMap. It is similar to HashMap except that it uses reference equality when comparing elements.

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Q415. Does an ArrayList allow elements of different types ? If not, Why the following code works List list1 = new ArrayList<>(); list1.add(1); list1.add("1");

Core Java

Ans. With Java 7 or Later. If you don't declare the list to be of specific type , it treats it as list of objects. int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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Q416. What are design situations to use Singleton and Prototype Design Pattern ?

Design

Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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Q417. What is wrong with the following if statement ?

if(x==y || x.equals(y) {
}

Core Java

Ans. if x==y turns out to be true x.equals(y) will be true too. If x.equals(y) could be true even if x==y is true or not.

So the only possible outcomes are

1 || 1 = 1
0 || 1 = 1
0 || 0 = 0

i.e the outcome of x.equals(y)

check for x==y is not required in this if statement.

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Q418. What is wrong with the following if statement ?

if(x==y && x.equals(y) {
}

Core Java

Ans. x==y means that both references have same type and are pointing to same memory location and hence would always mean that they have same value.

x.equals(y) is not required in this case.

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Q419. Difference between Hot and Cold Deployment ?

Server

Ans. Cold Deployment is a conventional deployment mechanism that follows the multi step process to deploy code changes to the running app i.e Build -> Deploy - Restart.

whereas

Hot Deployment is deployment changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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Q420. What is Hot Deployment ?

Server

Ans. It is the ability to deploy changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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