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Q1001. 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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Q1002. Write a program that identifies numbers in a list that are palindrome and perfect square ?

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Q1003. 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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Q1004. Explain Java collections

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

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Q1005. 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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Q1006. 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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Q1007. 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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Q1008. 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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Q1009. Find Intersection/union between two arrays.

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Q1010. Find unique values between two arrays using single for loop ?

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Q1011. Make "I Know Java" as "I Java Know" without using any inbuilt functions.

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Q1012. Find out the max and min number from given array

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Q1013. 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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Q1014. What is the difference between round and scale method of BigDecimal ?

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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Q1015. Which of the Core Java functions / packages / concept do you believe have become irrelevant in today's market ?

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Q1016. Sort a List of Objects using comparable and comparator

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Q1017. can we use null as keyword ?

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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Q1018. what is directive ?

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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Q1019. Which is the best collections for maintaining elements in an order ?

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Q1020. What is Dynamic Binding ?

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

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Q1021. How do we do Inheritance in Java ?

Ans. By extending class or implementing interface.

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Q1022. Difference between 32 bit and 64 bit JVM ?

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Q1023. Tell about shallow and deep cloning ?

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Q1024. Difference between final and finally

Ans. final can be used for variables , methods and class. A final variable cannot be changed , a final method cannot be overridden , a final class cannot be inherited.

Finally is a block which is used after Try and catch, a finally block is always executed.

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Q1025. What will happen if there is an exception in Java finally block ?

Ans. The regular behavior of exception handling will occur. It will look for any immediate catch handler and if none is provided, it would be transmitted to the callers until a catch handler is found or it's out of main function.

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Q1026. What is the default execution method in Java?

Ans. public static void main(String[] args)

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Q1027. Can methods without a return type be declared in Java? Is there a difference between void return type and no return type ?

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Q1028. how is the internal code for the "volatile" implemented ?

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Q1029. Write Java code that would cause deadlock ?

Ans. https://howtodoinjava.com/java/multi-threading/writing-a-deadlock-and-resolving-in-java/

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Q1030. is Java top down programming language or bottom up programming language?

Ans. bottom up programming language

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