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

Interview Questions and Answers - Order By Newest

Q1231. What are the advantage of Abstract classes over interfaces with respect to Java 7 ? and What changed in Java 8 to help facilitate that in Java 8 ?

Core Java

Ans. Abstract Classes provide default implementations of methods that are inherited by the classes that extend them, which was not the case for Interfaces. This changed in Java 8, where default implementations are provided for methods.

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Q1232. Why do we use Thread Class as well as Runnable Interface for creating threads in Java ?

Core Java

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Q1233. Why can we have a static inner class but not a static Top level class in Java ?

Core Java

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Q1234. Write a Program to print fibonacci series using recursion.

Core Java

Ans. public class FibonacciUsingRecursion {
   public static void main(String[] args) throws IOException{
      getNextFibanocci(1,1);
   }

   static int getNextFibanocci(int a,int b){
      if(a+b >= 100){
         return 0;
      } else {
         System.out.println(a+b);
         getNextFibanocci(b,a+b);
      }

      return 0;
   }
}

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Q1235. Can we use primitive types with Collection classes ?

Core Java

Ans. No, As collection classes involve use of Generics, they cannot accept primitive types.

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Q1236. Is immutability an advantage with Wrapper classes over primitive types ?

Core Java

Ans. There is no concept of de referencing with primitive types and hence they are implicitly immutable. Having wrapper classes as mutable offers disadvantages compared to primitive types. Wrapper classes being immutable offer similar advantage as primitive types.It actually overshadows the disadvantage wrapper class could have if they are immutable.

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Q1237. Do we have Integer constant pool of primitive int or Integer objects ?

Core Java

Ans. It's of Integer objects and not primitive int.

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Q1238. Which objects are eligible for garbage collection ?

Core Java

Ans. Objects that have lost their reference i.e. they cannot be accessed/used by the program anymore.

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Q1239. Do we have sorted collection for List ?

Core Java

Ans. Not in java.util

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Q1240. What is a BlockingQueue ?

Core Java

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Q1241. Which immutable classes have you worked with ? Can you name some immutable Collections ? How to make an immutable collection ?

Core Java

Ans. string and wrapper class objects

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Q1242. What are the benefits of immutability or Immutable classes ?

Core Java

Ans. Immutable objects are thread-safe so you will not have any synchronization issues.Immutable objects are good for Map keys and Set elements, since these typically do not change once created.Immutability makes it easier to write, use and reason about the code (class invariant is established once and then unchanged)Immutability makes it easier to parallelize your program as there are no conflicts among objects.The internal state of your program will be consistent even if you have exceptions.References to immutable objects can be cached as they are not going to change.

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Q1243. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

Core Java

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Q1244. How ConcurrentHashMap provides better performance compared to HashTable ?

Core Java

Ans. ConcurrentHashMap uses multiple buckets to store Data and hence avoid read locks which facilitates better performance.

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Q1245. What are annotations and what are it's advantages ?

Core Java

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Q1246. Suppose we have a string "Java is object oriented language" and we have to reverse every alternate word in string. How would we do that using Java program.

Core Java

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Q1247. How to convert array to list in Java ?

Core Java

Ans. We can use Arrays.asList

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Q1248. How much by default filling ratio in HashMap ?

Core Java

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Q1249. Can we override wait() or notify() ?

Core Java

Ans. No, because these are final.

public final void wait() throws InterruptedException

public final void notify()

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Q1250. What is a double ended queue?

Core Java

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Q1251. A Kid can go up 1, 2 or 3 stairs in one step. Write a method that takes number of steps in a stair will print all possible ways he can take.

For example , printAllCombinations(3) should print

111
12
21
3

Similarly , printAllCombinations(4) should print

1111
121
13
211
22
31
4

Core Java

Ans. public static String findStep(int n) {
if (n == 1 || n == 0)
return 1;
else if (n == 2)
return 2;
else
return findStep(n - 3) + findStep(n - 2) + findStep(n - 1);
}

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Q1252. Write a method that takes an integer and verifies if the number is power of 10.

Core Java

Ans. public static boolean isPowerOfTen(long input) {

if (input % 10 != 0 || input == 0) {
return false;
}

if (input == 10) {
return true;
}

return isPowerOfTen(input/10);
}

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Q1253. What is the default data type of state variables in Clonable interface and Serializable interface ?

Core Java

Ans. Cloneable and Serializable are Marker Interfaces, So these are empty interfaces with no variables.

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Q1254. What are falsy attributes in javascript ?

Javascript

Ans. A falsy value is something which evaluates to FALSE, for instance when checking a variable. There are only six falsey values in JavaScript: undefined, null, NaN, 0, "" (empty string), and false of course.

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Q1255. Difference between Scriptlet and JSTL.

Javascript

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Q1256. How can i split a linked list in two parts in java 8?

Core Java

Ans. This can be done using a Spliterator.

LinkedList list = Arrays.asList("names","numbs","birds","animals");
Spliterator split1 = list.Spliterator();
Spliterator split2 = split1.Spliterator();

Now, the LinkedList is split into split1 and split2.
use split2 first then split1 to check the output.

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Q1257. how does abstraction help your application ?

Core Java

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Q1258. Explain OOps concepts.

Core Java

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Frequently asked in Genpact.

Q1259. What is object cloning ?

Core Java

Ans. Its is the process of creating exact copy of an object being cloned. In Object class one native method called clone() is there which is meant for Shallow Cloning of Object. Shallow cloning means bitwise copy of an object.In case of primitive data type it will create an exact copy of primitive values as well as variables but if the object contains any reference of an object then it will not copy the referenced object rather it will create the copy of reference variable and assigned it to the old object.

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Q1260. What are different methods to get the permanent gen space of running application?

Core Java

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