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

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Q421. What is Jenkins ?

Jenkins

Ans. It is a continuous integration tool written in Java.

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Q422. What is Nagios ?

Ans. Nagios is open source system , network and infrastructure monitoring software application. It alerts the user if anything goes wrong. Nagios is widely used as monitoring tool for enterprise applications.

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Q423. Write code explaining use of Scanner class ?

Ans. Scanner sc = new Scanner(System.in);
int i = sc.nextInt();

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Q424. In which cases isn't instanceof operator a bad practice?

Core Java

Ans. To avoid ClassCastException.

Though the following code will compile fine but will result in ClassCastException during runtime.

Fruit fruit = new Apple();
Banana banana = Banana(fruit); // ClassCastException

This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception.

This exception can be avoided by following code.

Fruit fruit = new Apple();
if(fruit instanceOf Banana){
Banana banana = Banana(fruit); // ClassCastException
}

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Q425. Difference between Scanner and BufferedReader ? Which one is faster and Why ?

Core Java

Ans. Scanner is used for parsing tokens from the contents of the stream while BufferedReader just reads the stream.

BufferedReader read files efficiently by using a buffer to avoid physical disk operations.

Buffer size of Scanner is usually smaller than the Buffered Writer.

BufferedReader is faster that Scanner as it just reads the Stream and doesn't Parse the tokens to read the stream into primitive data types.

Sample Code for Scanner

Sample Code for BufferedReader

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Q426. Which sorting algorithm is used by Collections.sort() in Java ?

Core Java

Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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Q427. What doesn Http keep alive header does ?

Java EE

Ans. Http is connection less by default. header informs hosts to keep the connection alive so that the same connection can be reused for multiple communication.

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Q428. Difference between HashMap and WeakHashMap ?

Ans. WeakHashMap uses weak reference for keys, which means if the key object doesn't have any reference then both key/value mapping will become eligible for garbage collection.

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Q429. Which tree is used to implement TreeMap in Java?

Ans. Red Black Tree

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Q430. What is collision in hash collections ?

Core Java

Ans. Collision is the situation when two different elements have the same Hash Code.

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Q431. What will the following code result ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get(null));

Ans. Compile time error at last line as the get method expect argument of type native int.

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Q432. What will the following code result ? Will it compile ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get((Integer)null));

Ans. Yes but the last line will throw NullPointerException upon execution.

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Q433. What is OutOfMemoryError in Java?

Core Java

Ans. OutOfMemoryError in Java is a subclass of VirtualMachineError and is thrown by JVM when it runs out of heap memory.

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Q434. Do you know of any facility to convert between Scala and Java Util Collections ?

Scala

Ans. We can use JavaConversions which is a part of Scala Library.

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Q435. Which interfaces are implemented by BatchUpdateException?

Ans. [Iterable]

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Q436. If we add Enum constants to a sorted collection ( Treemap , TreeSet ), What will be the order in which they will be maintained ?

a. Sorted Collection wont maintain them in any order.
b. Insertion Order
c. Order in which constants are declared.
d. Natural Sorting Order.

Ans. Order in which constants are declared.

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Q437. Which interface does java.util.Hashtable implement ?

a. List
b. Set
c. Collection
d. Map

Core Java

Ans. Map

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Q438. Which of the following is false ?

a. HashMap came before HashTable.
b. HashMap allows null values whereas Hashtable doesnâ€™t allow null values.
c. HashTable and HashMap allow Key-Value pairs.
d. Hashtable is synchronized whereas HashMap is not.

Ans. HashMap came before HashTable.

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Q439. Which of the following is true ?

a. We can serialize static variables
b. We can serialize transient variables
c. We can serialize final variables
d. We can serialize instance methods

Ans. We can serialize final variables

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Q440. Which of the collections allows null as the key ?

a. HashTable
b. HashMap
c. TreeMap
d. LinkedHashMap

Core Java

Ans. HashMap

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Q441. Why should we have Javascript method definitions within HTML Head section ?

a. Its safe to have javascript code within head section
b. Head section gets loaded even if there is any error in loading HTML page
c. Head section gets executed first and hence assure that js method definition will be loaded before they are called
d. So that we can have method definition and method call at the same place

Ans. Head section gets executed first and hence assure that js method definition will be loaded before they are called

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Q442. Effective Java 6 , TreeMap implements ...

a. Map Interface
b. SortedMap Interface
c. NavigableMap Interface
d. SortedNavigableMap Interface

Ans. SortedMap Interface

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Q443. Which of the following is not possible ?

a. try block followed by catch
b. try block followed by finally
c. try block followed by catch block and then finally
d. try block without catch or finally block

Ans. try block without catch or finally block

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Q444. Invoking start twice on same thread leads to ..

a. ClassCastException
b. NullPointerException
c. InterruptedException
d. IllegalStateException

Ans. IllegalStateException

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Q445. What is the input to the Reduce function ?

a. One Key and One Value
b. Multiple Keys and Multiple associated Values
c. Multiple Keys and One associated values with each
d. One key and associated values.

Ans. One key and associated values.

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Q446. Which of the following Interface needs to be implemented by any object that wishes to be notified of the ApplicationContext that it runs in ?

a. ApplicationContextAware
b. ApplicationContextUtils
c. ApplicationContext
d. Aware

Spring

Ans. ApplicationContextAware

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Q447. What is RI or Reference Implementation ?

Ans. RI or Reference Implementation is a sample implementation provided for the API's / Specs, usually by their developers. This is usually a part of API documentation.

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Q448. Explain Application / Server architecture being used in your project ?

or

Explain your project architecture ?

Ans. We are using cluster of Web servers and Application servers. Load Balancer is used to manage the load between them. Down the layer we have middleware server and then DB server to access database.

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Q449. How do you monitor the server resources if inadvertently high traffic is reported ?

Ans. We use SAR command for that purpose. We also have GUI system monitoring tool to keep real time check of requests, load and memory usage.

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Q450. Have you ever faced any problem due to caching?

Ans. Yes , sometime we receive issues related to outdated pages being rendered to the user. In those cases we clear the cache and then try to investigate the reason for that. Sometime the issue is due to comparatively high refresh interval. In those cases we reduce the cache refresh interval.

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