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Q271. Difference between TreeMap and SortedMap ?

Ans. sortedMap is an interface ,while TreeMap is an implementation of sortMap.

We can not create an instance of sortedMap but we can create an instance of treeMap

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Q272. Difference between ArrayList and HashSet ?

Core Java

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q273. difference between ArrayList and array ?

Core Java

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q274. What is the difference between final and static in java ?

Core Java

Ans. final keyword is used to restrict the user from modifying the variable, extending the class and overriding a method

static keyword is used for memory management which can be used for variable, class, method where in it belongs to the class not to the instance of object

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Q275. What is the difference between Encapsulation and encryption ?

Networking

Ans. Encapsulation is the process of wrapping the data with another layer to be transported across the network with the source and destination details on just like the analogy of wrapping letter in envelope with the source and destination details on the envelope. Encryption on the other hand is the process of hashing text or transforming the data in a form that is not readable except you have access to the key use to decrypt it.

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Q276. Why is String a class in Java ?

Core Java

Ans. 1. Creating a class helps in specifying operations on the Strings like length , sub string , concatenation etc.

2. It acts as a Wrapper class for "Array of Characters" and hence facilitates it's usage in collections, assignment to null.

3. Immutability of String objects facilitates in reuse , security and caching.

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Q277. Difference between equals and compareTo in Java ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal.

The compareTo() method is used for comparing two objects in Java. It is usually defined for the classes whose objects needs to be ordered through Comparable interface or need to be part of an ordered collection like TreeSet or TreeMap.

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Q278. Is ConcurrentHashMap synchronized ?

Core Java

Ans. Yes, ConcurrentHashMap is synchronized.

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Q279. Is HashMap Synchronized ?

Core Java

Ans. No HashMap isn't synchronized. ConcurrentHashMap and Hashtable are synchronized.

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Q280. Can we use Param Store with AWS Lambda ?

Amazon Web Services (AWS)

Ans. Yes

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Q281. What measures would you take to avoid Java threading issues in a multi-threaded environment ?

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Q282. Does abstract class have public constructor?

Core Java

Ans. Yes, an abstract class can have a constructor in Java.

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Q283. Explain CloneNotSupportedException ?

Core Java

Ans. If we do not mention, Cloneable Interface to the Class which we want to Clone then we get this exception, only if we try to clone an object

Like:
public class TestClone{
@Override
   protected Object clone() throws CloneNotSupportedException {
      return super.clone();
   }
}

In Main, You try to do:
TestClone clone = new TestClone();

      TestClone clone2 = (TestClone) clone.clone();

You will get CloneNotSupportedException.

Just add -> public class TestClone implements Cloneable {

and things are fixed.

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Q284. Why Hadoop serialized data types are not using in Spark serialization ?

BigData

^{This question was recently asked at 'Tavant Technology'.This question is still unanswered. Can you please provide an answer.}

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Q285. Explain when you would decide to use open authentication ?

Authentication

Ans. Google OAuth can be used when we want to grant the access of our google credentials to the service provider ( most likely a cloud-based mobile application) by using the option ' Login via Google'

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Q286. What does 'variable hoisting' mean?

JavaScript

Ans.

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Q287. How many heaps will be there with 3 threads ?

Core Java

Ans. All threads share a common heap.

Each thread has a private stack, which it can quickly add and remove items from. This makes stack based memory fast, but if you use too much stack memory, as occurs in infinite recursion, you will get a stack overflow.

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Q288. Please explain the architecture of our application through a diagram ?

General

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Q289. What are the disadvantages of binary search trees?

Algorithm

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Q290. How to write an iterator for an iterator of iterators?

Core Java

Ans. CustomArrayList myarrayList = new CustomArrayList();
      myarrayList.add("Value 1");
      myarrayList.add("Value 2");
      myarrayList.add("Value 3");

      for (String string : myarrayList) {
         System.out.println(string);
      }

package sample.utils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class CustomArrayList implements Iterable {

   private ArrayList mylist = new ArrayList();

   public void add(T t) {
      this.mylist.add(t);
   }

   @Override
   public Iterator iterator() {
      return new CustomIterator(mylist);
   }

   class CustomIterator implements Iterator {

      private int indexPosition = 0;
      private List internalList;

      public CustomIterator(List internalList) {
         this.internalList = internalList;
      }

      @Override
      public boolean hasNext() {
         if (internalList.size() >= indexPosition 1) {
            return true;
         }
         return false;
      }

      @Override
      public E next() {
         E val = internalList.get(indexPosition);
         indexPosition ;
         return val;
      }

   }

}

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Q291. Do you think it's a good practice to keep passwords in config files ?

Solution

Ans. We can keep them in config as encrypted values.

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Q292. Can we keep application configuration at different places and what could be the consideration for choosing multiple places for doing so ?

Design

Ans. Yes an application can have configuration stored at multiple places. Factors that could facilitate such a design could be

1. Type of config information - We may have a case to store confidential information differently than other regular config value

2. Environment - We may like to have a base config ( defined in application package ) and then a different override mechanism in different environments.

3. Centralization - Sometime some configs need to be shared across application and hence centralized.

4. Testing - Testing against config may not be possible in some enviornments in certain cases and hence additional config store might be kept for testing purpose only.

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Q293. Write a calculator and find if a character appears more than n times ?

Design

^{This question was recently asked at 'Mercury Systems'.This question is still unanswered. Can you please provide an answer.}

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Q294. How would you test a Twitter application ?

Testing

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Q295. Implement a queue, using only stacks

Data Structure

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Q296. Code an elevator simulator.

Design

^{This question was recently asked at 'TrustArc'.This question is still unanswered. Can you please provide an answer.}

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Q297. What is the minimum number of tables required to perform a SQL join?

Database

Ans. 1 , We can do self join

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Q298. What is a difference between JUnit 3 and 4 ?

Junit

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Q299. Can we have a final argument in a method ? What is the use of that if we do so ?

Core Java

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Q300. why is "".equals(str); safer than str.equals("")?

Core Java

Ans. str.equals("") this statement will throw NullPointerException if str is null where as "".equals(str) works fine even if str is null

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