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Q271. 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.

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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Q272. Find out the max and min number from given array

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Q273. Make "I Know Java" as "I Java Know" without using any inbuilt functions.

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Q274. Find Fibonacci first n numbers using recursion ?

Ans. public int fibonacci(int n) {
if(n == 0)
return 0;
else
if(n == 1)
return 1;
else
return fibonacci(n - 1) fibonacci(n - 2);
}

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Q275. Find unique values between two arrays using single for loop ?

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Q276. Find Intersection/union between two arrays.

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Q277. Can we change return type of Overridden method ?

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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Q278. What is garbage collection ?

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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Q279. When to use List, Set and Map in 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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Q280. Get all numbers from a collection that are both perfect square and palindome

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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Q281. Explain Java collections

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

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Q282. Write a program to sort the Array of Strings

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

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Q283. Write a program that identifies numbers in a list that are palindrome and perfect square ?

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Q284. Can you explain filter and collectors in java 8 ?

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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Q285. Can you explain filter and collectors in java 8 ?

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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Q286. Why do we need to close the Scanner ?

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

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Q287. What is the difference between instantiation and initialization ?

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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Q288. Describe inheritance and polymorphism and their importance for OOP.

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Q289. Design a class that find all files with SSN.

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Q290. Are getters setter / accessor mutator methods instance methods or static methods ? why ?

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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Q291. What are the different types of methods in Java ?

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

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Q292. 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.

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Q293. Write code to get count of every 5 letter word in a string using lambda expression

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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Q294. Have you used any framework to capture command line arguments or options ?

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Q295. Have you worked on creating any cron job ?

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Q296. 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 ?

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Q297. What is the advantage of BidDecimal over Double ?

Ans. BigDecimal provides more precision as compared to double.

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Q298. What will the following code return

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

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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Q299. What are we doing here

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

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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Q300. Can you explain following exception

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

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