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

Interview Questions and Answers - Order By Newest

Q1341. Can we have private methods in interfaces ?

Core Java

Ans. Yes, With Java 9

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Q1342. What could be the reason for allowing private methods in java 9 ?

Core Java

Ans. Java 8 allowed for method implementation using default methods in interfaces. As those default methods could contain complex logic and might need organizing the logic into multiple methods, they have allowed for private methods.

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Q1343. What is the difference between implementing interfaces and inheritance in Java ?

Core Java

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Q1344. What is a weak reference ?

Core Java

Ans. A weak reference is a reference that gets removed on the next garbage collection cycle.

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Q1345. Write a program that count the number of access to a method?

Core Java

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Q1346. Can you explain following exception

java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

Core Java

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Q1347. What are we doing here

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getelement2)));

Core Java

Ans. We are averaging elements of a collection by element1 grouped by element1

* list is the reference of collection
* element1 is the member element returned by getElement1 method of ClassA
* element2 is the member element returned by getElement2 method of ClassA

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Q1348. What will the following code return

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getElement2)));

Core Java

Ans. Map<DataType1,DataType2> where DataType1 is the data type of element1 ( returned by getelement1 method ) and DataType2 is the data type of element2 ( returned by getElement2 method )

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Q1349. What is the advantage of BidDecimal over Double ?

Core Java

Ans. BigDecimal provides more precision as compared to double.

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Q1350. What is the difference between following rounding modes

RoundingMode.CEILING
RoundingMode.DOWN
RoundingMode.FLOOR
RoundingMode.HALF_DOWN
RoundingMode.HALF_UP
RoundingMode.HALF_EVEN

Which is the one you use often and Why ?

Core Java

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Q1351. Have you worked on creating any cron job ?

Core Java

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Q1352. Have you used any framework to capture command line arguments or options ?

Core Java

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Q1353. How would you choose your favorite company name for e.g. three companies are given in radio buttons Infosys, TCS and Aricent. Do You need to loop trough all radio buttons and select your favorite company or can just get the selected value.

Javascript

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Q1354. Write code to get count of every 5 letter word in a string using lambda expression

Core Java

Ans. String str = "I had been saying that he had been there";

Map<String,Long> countWords = Arrays.asList(str.split(" ")).stream().filter(p->p.length() = 5).collect(Collectors.groupingBy(p->p,Collectors.counting()));

System.out.println(countWords);

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Q1355. Can you write code so that we can keep track of Keys that have their values changed along with the number of times they were changed.

Core Java

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Q1356. What are the different types of methods in Java ?

Core Java

Ans. Static Methods
Instance Methods
Accessor / Mutator or getter setters

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Q1357. Are getters setter / accessor mutator methods instance methods or static methods ? why ?

Core Java

Ans. They are usually instance methods. They are usually applied to DAOs / DTOs / POJO that are used to transport objects and used to access object elements. As they are tied to objects and are not common to all objects of a class, hence they are created as non static.

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Q1358. Design a class that find all files with SSN.

Core Java

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Q1359. Describe inheritance and polymorphism and their importance for OOP.

Core Java

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Q1360. What is the difference between instantiation and initialization ?

Core Java

Ans. Instantiation is the process of reserving memory for the object

For ex -

List list = new ArrayList();

Initialization is the process of setting the default value for the object or default object construction.

List list = new ArrayList(set);

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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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