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Core java - Interview Questions and Answers for 'Amazon' - 16 question(s) found - Order By Newest

Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.
  Q1. What are the difference between composition and inheritance in Java?Core Java
Admin
info@buggybread.com
Ans. Composition - has-a relationship between objects.
Inheritance - is-a relationship between classes.

Composition - Composing object holds a reference to composed objects and hence relationship is loosely bound.
Inheritance - Derived object carries the base class definition in itself and hence its tightly bound.

Composition - Used in Dependency Injection
Inheritance - Used in Runtime Polymorphism

Composition - Single class objects can be composed within multiple classes.
Inheritance - Single class can only inherit 1 Class.

Composition - Its the relationship between objects.
Inheritance - Its the relationship between classes.

  Sample Code for inheritance

  Sample Code for composition

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   Like         Discuss         Correct / Improve     java   java concepts   inheritance  object oriented programming (oops)  oops concepts   composition  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts vs composition  object oriented programming (oops)  oops concepts     Asked in 28 Companies      basic        frequent

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Very frequently asked to Fresh graduates.
  Q2. What is the difference between Encapsulation and Abstraction?Core Java
Anonymous
Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

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   Like         Discuss         Correct / Improve     java   oops   oops concepts   encapsulation  object oriented programming (oops)  oops concepts   abstraction   basic interview question     Asked in 10 Companies      basic        frequent

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q3. What is the difference between ArrayList and LinkedList ?Core Java
admin
info@buggybread.com
Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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   Like         Discuss         Correct / Improve     collections   java   data structures   arraylist   linkedlist     Asked in 61 Companies      Basic        frequent

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Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.
  Q4. Differences between abstract class and interface ?Core Java
Admin
info@buggybread.com
Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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   Like         Discuss         Correct / Improve     java   classes   abstract class   interfaces     Asked in 65 Companies      basic        frequent


Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback)
  Q5. Describe, in general, how java's garbage collector works ?Core Java
Anonymous
Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.

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   Like         Discuss         Correct / Improve     java   garbage collection   java memory management   advanced     Asked in 21 Companies      intermediate        frequent

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 Q6. Write a program to print the index of the first non repeated character in a java stringCore Java2017-01-27 18:30:21

Ans. public class BuggyBread1{
public static void main (String args[]) {
   String str = "hheello world";
   char[] charArray = str.toCharArray();
   char selectedChar = 'a';
   for(char char1: charArray){
      if(!str.contains(Character.toString(char1).concat(Character.toString(char1)))){
         selectedChar = char1;
         break;
      }
   }
   System.out.println(str.indexOf(Character.toString(selectedChar)));
}
}

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   Like         Discuss         Correct / Improve     string  code  coding     Asked in 9 Companies


  Q7. Write a Program to check if 2 strings are Anagrams ?Core Java2016-11-30 20:52:37

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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   Like         Discuss         Correct / Improve      check if 2 strings are Anagrams     Asked in 30 Companies      basic        frequent


 Q8. How would you count the number of words in a string consisting of uneven number of spaces between words( not dictionary words)? With and without library functions.Core Java2016-11-30 20:46:12

Ans. package com.string;

import java.util.Scanner;

public class String13 {
public static void main(String[] args) {
System.out.println("Enter Sentence");
Scanner sc=new Scanner(System.in);
String sentence=sc.nextLine();
String[] words=sentence.split(" ");
int count=0;
for (String string : words) {
string.trim();
if(!string.equals("")){
count++;
System.out.println(string " " count);
}
}
}
}

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   Like         Discuss         Correct / Improve     code  coding     Asked in 1 Companies


Frequently asked in high end product companies.
 Q9. Write code for LRU CacheCore Java2017-01-10 10:15:17

Ans. https://www.geeksforgeeks.org/lru-cache-implementation/

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   Like         Discuss         Correct / Improve     cache  LRU cache  coding  code     Asked in 10 Companies      intermediate


 Q10. Given array of integers, find first two numbers that adds up to 10.Core Java2017-03-03 14:27:38

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     Code  Coding     Asked in 1 Companies


 Q11. Write a program to reverse words of a sentence.Core Java2017-03-03 14:30:14

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     code  Coding     Asked in 1 Companies


 Q12. how to get most significant bit from a byte?Core Java2017-03-03 14:37:39

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve          Asked in 1 Companies


 Q13. Given a string with multiple opening and closing brackets, determine if the string is valid or not ( to see if the string has all closing brackets for each opening bracket ) ?Core Java2017-05-07 20:10:10

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     code  coding     Asked in 1 Companies


 Q14. Given a string and index for the opening bracket, find the index of matching closing bracket. Core Java2017-05-07 20:11:06

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     matching bracket  stack     Asked in 1 Companies


 Q15. Explain how Mark & Sweep is implemented in garbage collection.Core Java2018-02-08 13:19:44

 This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve          Asked in 1 Companies


  Q16. Find Intersection/union between two arrays.Core Java2018-05-13 19:40:34

 This question was recently asked at 'Bristlecone,Amazon Lab126,Amazon,Microsoft,Facebook,NCR,Google'.This question is still unanswered. Can you please provide an answer.


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   Like         Discuss         Correct / Improve     arrays  code  coding     Asked in 7 Companies        frequent




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