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Very Frequently asked to Senior Software Engineers or Developers.

Q461. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Q462. If everything is an object , Cant we declare every object as

Object obj = new String();

Core Java

Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.

We cannot access methods defined in String class or in any class in hierarchy between String and Object.

For example - we cannot do obj.append("abc") as it will now give compile time error.

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Q463. Which type of memory is cleaned / recovered by garbage collection - stack or heap ?

Core Java

Ans. Heap memory.

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Q464. Write a program to print all even numbers first and then all odd numbers till 100. For example the output should be
2
4
6
8
...... 100
and then
1
3
5
7
...... 99

using only 1 for loop ? Is it possible with just one loop ?

Core Java

Ans. Yes , It can be done using single for loop

public class BuggyBread{
public static void main (String args[]) {
   int x = 50;
   for(int i=1;i <= 100;i++){
      if(i<=50){
         System.out.println(i*2);
      } else {
         System.out.println(i-x);
         x = x - 1;
      }
   }
}
}

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Q465. Given two files with list of words, write a program to show the common words in both files

Core Java

Ans. import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.io.*;
public class Common {
public static void main(String ar[])throws Exception
   {
      File f=new File("a.txt");
File f1=new File("x.java");
      System.out.println(f.exists());
FileInputStream fin = new FileInputStream(f);
      FileInputStream fin1 = new FileInputStream(f1);

      byte b[]=new byte[10000];
byte b1[]=new byte[10000];
fin.read(b);
fin1.read(b1);
String s1 = new String(b);
String s2 =new String(b1);

String words1[] = s1.trim().split(" ");
String words2[] = s2.trim().split(" ");
Listlist1 = new ArrayList<>(Arrays.asList(words1));
Listlist2 = new ArrayList<>(Arrays.asList(words2));
list1.retainAll(list2);
System.out.println(list1);
}
}

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Q466. What is the difference between for and foreach loop in java ? Which one should be used in which cases ?

Core Java

Ans. 1. for loop in java is used with a counter as following

for(int counter=0;counter < 50;counter++){
System.out.println(list.get(counter));
}

for iterating and printing the contents of a collection

whereas foreach loop can be specified directly without the use of counter

for(String str:list){
System.out.println(list.get(counter));
}

2. for Each loop syntax is more clean if we have to iterate over the elements of a collection and we need not keep track of the record count

3. For is preferred when we need loops without the usage of collections or Array of objects and entirely primitives are being used

4. for loop is preferred if we need to keep track of record count and have to perform some action of the basis of that. For example - If we have to print something after every 5 records, With for each loop in such case, we will have to keep a separate counter.

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Q467. Does java supports operator overloading ?

Core Java

Ans. No

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Q468. What is database Normalization ?

Database

Ans. https://en.wikipedia.org/wiki/Database_normalization

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Q469. When is the situation when finally section won't execute ?

Core Java

Ans. If the process / app is abruptly killed or terminated.

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Q470. What is the use of static keyword in Java ?

Core Java

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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Q471. Explain various Searching and Sorting Algorithms ?

Algorithm

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Q472. Is it a good practice to use Asterick(*) in import statement to load multiple packages with single import statement ?

Core Java

Ans. No, we should be lean in loading only packages which are required. Loading packages which are not being used result in memory overheads.

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Q473. What is a Servlet Filter ?

Java EE

Ans. It's an object that can intercept http request and response and hence we can take appropriate action on those requests.

There are different types of filters based on Specifications like

Authentication
Logging
Encryption
Tokenizing

etc

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Q474. Can we override wait() or notify() methods?

Core Java

Ans. wait and notify are declared final in object class and hence cannot be overridden.

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Q475. Write an algorithm / Java Program to show duplicates in an array of n elements?

Algorithm

Ans. int duplicateArray[] = { 1, 2, 2, 3, 4, 5, 6, 8, 9}
Set unique = new HashSet();
for (int i = 0; i < duplicateArray.length; i) {
if (unique.contains(duplicateArray[i])) {
System.out.println(duplicateArray[i]);
} else {
unique.add(duplicateArray[i]);
}
}

Complexity O(n) = nHashSet contains and add has O(n) = 1

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Q476. What is a binary tree ?

Algorithm

Ans. Binary tree is a tree in which each node has up to two children.Tree is a data structure composed of nodes.Each tree has a root node(not necessary in graph theory). The root node has zero or more child nodes.Each child node has zero or more child nodes, and so on.The tree cannot contain cycles.

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Q477. What is the difference between authentication and authorization ?

Authentication

Ans. Authentication is the process of verifying the identity and credentials of the user to authenticate him into the system.

whereas

Authorization is the process by which access to a segment , method or resource is determined.

Authorization is usually a step next to authentication.

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Q478. Write a multi threaded Program that will simulate transferring of money across accounts ?

Core Java

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Q479. Write a Program to print factorial of a number using recursion

Core Java

Ans. public class BuggyBread {
public static void main(String args[]) {
System.out.println(factorial(5));
}

private static int factorial(int number){
if(number == 1){
return 1;
} else {
return number * factorial(number - 1);
}
}
}

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Q480. What is a Webdriver ?

Testing

Ans. Selenium WebDriver is a tool for automating web application testing.It helps in replicating the manual tester behavior like keyboard entry, mouse events etc and then matching the output against the expected.

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Q481. How would you do an object oriented design on animals in a zoo ?

Design

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Q482. What access the variable gets if we don't provide any access specifier ?

Core Java

Ans. It gets the default access i.e package protected.

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Q483. What is Amazon S3 ?

Amazon Web Services (AWS)

Ans. Amazon Simple Storage Service or S3 is object storage with a simple web service interface to store and retrieve any amount of data from anywhere on the web.

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Q484. Do you like Native SQL Apis like JDBC or JPA / Hibernate ?

Hibernate

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Q485. How Marker interfaces works internally ?

Core Java

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Q486. Can we overload abstract methods ?

Core Java

Ans. Yes

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Q487. What are the ways in which an application can maintain config variables ?

Ans. 1. Property files
2. config xml
3. Database

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Q488. How will you design a Log4j kind of framework.

Log4j

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Q489. Difference between log4j and slf4j ?

Logging

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Q490. Difference between Virtual Memory and Demand Paging?

Operating System

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