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

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Q1361. Why do we need to close the Scanner ?

Core Java

Ans. For releasing input stream reference (System.in), you should close scanner.

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Q1362. Can you explain filter and collectors in java 8 ?

Core Java

Ans. Filters are used to filter object in stream on certail criteria. And collector is used to collect outcome of the stream. Collector is a terminal operation.
List numbers = List.of(1,2,3,4,5,6,7);
List evenNumbers = numbers.stream().filter(n -> n%2==0).collect(Collectors.toList());
The above code will filter out odd numbers and return the list of even number.

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Q1363. Can you explain filter and collectors in java 8 ?

Core Java

Ans. Filters are used to filter object in stream on certain criteria.
Collector is used to collect outcome of the stream. Collector is a terminal operation.
List numbers = List.of(1,2,3,4,5,6,7);
List evenNumbers = numbers.stream().filter(n -> n%2==0).collect(Collectors.toList());
The above code will filter out odd numbers and return the list of even number.

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Q1364. Write a program that identifies numbers in a list that are palindrome and perfect square ?

Core Java

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Q1365. Write a program to sort the Array of Strings

Core Java

Ans. String[] s = { "sort", "string", "array" };
Collections.sort(Arrays.asList(s));
System.out.println(Arrays.toString(s)); // [array, sort, string]

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Q1366. Explain Java collections

Core Java

Ans. Collection is a container which is used to store and manipulate the group of objects

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Q1367. Get all numbers from a collection that are both perfect square and palindome

Core Java

Ans. public static void main(String[] args){
      List<Integer> listOfIntegers = Arrays.asList(1,2,3,4,5,6,7,8,9,10,11);
      List<Integer> perfectAndPalindromeIntegers = new ArrayList<Integer>();

      for(Integer i: listOfIntegers){
         if(isPalindrome(i) && isPerfect(i)){
            perfectAndPalindromeIntegers.add(i);
         }
      }

      System.out.println(perfectAndPalindromeIntegers);
   }

   private static Boolean isPalindrome(Integer i){
      String str = String.valueOf(i);

      char[] charArray = str.toCharArray();

      int x = 0;
      int y = str.length()-1;

      while(x < y){
         if(charArray[x] != charArray[y]){
            return false;
         }
      }

      return true;
   }

   private static Boolean isPerfect(Integer i){
      for(int x=2;x<3;x++){
         if(x*x == i){
            return true;
         }
      }

      return false;
   }

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Q1368. When to use List, Set and Map in Java

Core Java

Ans. I. If we want a Collection that does not store duplicate values, then we use a Set based collection.

II. If we want to frequently access elements operations based on an index value then we use a List based collection. E.g. ArrayList

III. If we want to maintain the insertion order of elements in a collection then we use a List based collection.

IV. For fast search operation based on a key, value pair, we use a HashMap based collection.

V. If we want to maintain the elements in a sorted order, then we use a TreeSet based collection.

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Q1369. What is garbage collection ?

Core Java

Ans. The garbage collection is a facility wherein a program runs on the Java Virtual Machine which gets rid of objects, which are not being used by a Java application anymore. It is a form of automatic memory management and recollection.

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Q1370. Can we change return type of Overridden method ?

Core Java

Ans. Yes, we can change return type of overridden method in child class but child's return type should be sub-type of parent's return type.

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Q1371. Find Intersection/union between two arrays.

Core Java

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Q1372. Find unique values between two arrays using single for loop ?

Core Java

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Q1373. Make "I Know Java" as "I Java Know" without using any inbuilt functions.

Core Java

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Q1374. Find out the max and min number from given array

Core Java

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Q1375. Math.round method rounds the decimal to an integer by stripping off the decimal places. How can we use the same method to keep only 2 decimal places

For example -

Math.round(12.3456) will return 12. What should we do to get 12.34 without using any other class or method.

Core Java

Ans. We can multiply the value by 100 and then use Math.round on that and then divide the result by 100

For example -

(Math.round(12.3456 * 100)) / 100

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Q1376. What is the difference between round and scale method of BigDecimal ?

Core Java

Ans. Round method would round it to integer places irrespective of if it's decimal places or not whereas scale would only round the decimal places.

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Q1377. Which of the Core Java functions / packages / concept do you believe have become irrelevant in today's market ?

Core Java

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Q1378. What is the difference between subscribe and blockingSubscribe method ?

RxJava

Ans. blockingSubscribe will block the current thread and wait till the chain completes

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Q1379. Difference between concatMap and flatMap ?

RxJava

Ans. Flatmap converts stream(s) into a single streams without maintaining a order where as concatmap does the same along with maintaining the order

flatmap example -[[1,2,3],[4,5,6],[7,8,9]] -> [1,4,7,2,5,8,3,6,9]

concatmap example -[[1,2,3],[4,5,6],[7,8,9]] -> [1,2,3,4,5,6,7,8,9]

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Q1380. What are the drawbacks of Reactive extensions ?

ReactiveX

Ans. Reactive extensions have a steep learning curve which makes it confusing for beginner and intermediate developers.

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Q1381. Sort a List of Objects using comparable and comparator

Core Java

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Q1382. can we use null as keyword ?

Core Java

Ans. null is a literal similar to true and false in Java. These are not keywords because these are the values of something. As null is the value of a reference variable, true is the value of a boolean variable.

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Q1383. what is directive ?

Core Java

Ans. A compiler directive is an instruction that tells the JVM how compilation should occur. A directive provides method-context precision in controlling the compilation process.

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Q1384. what is event handler script ?

JavaScript

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Q1385. How can java script access a database ?

JavaScript

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Q1386. Which statement is used to exit a function in java script ?

JavaScript

Ans. return

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Q1387. Which is the best collections for maintaining elements in an order ?

Core Java

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Q1388. What is Dynamic Binding ?

Core Java

Ans. Dynamic Binding happens at runtime. Method overriding is an example of Dynamic Binding

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Q1389. How do we do Inheritance in Java ?

Core Java

Ans. By extending class or implementing interface.

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Q1390. Difference between 32 bit and 64 bit JVM ?

Core Java

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