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Interview Questions and Answers for 'BlackRock' - 9 question(s) found - Order By Newest

Frequently asked in all types of companies especially Indian Services companies. Frequently asked in CTS (Based on 2 feedback)
  Q1. What is the use of hashcode in Java ?Core Java
Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not.

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   Like         Discuss         Correct / Improve     java   collections   hashcode   advanced  hashtable     Asked in 33 Companies      intermediate        frequent

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Frequently asked question for intermediate developers. Frequently asked in HCL Technologies and EPAM.
  Q2. What is Volatile keyword used for ?Core Java
Ans. Volatile is a declaration that a variable can be accessed by multiple threads and hence shouldnt be cached.

  Sample Code for volatile

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   Like         Discuss         Correct / Improve     java   oops   synchronization   volatile   java keywords     Asked in 42 Companies      intermediate        frequent

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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
  Q3. What is the difference between StringBuffer and String class ?Core Java
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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   Like         Discuss         Correct / Improve     java   string   stringbuffer   frequently asked     Asked in 18 Companies      basic        frequent

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 Q4. What is a ConcurrentHashMap ?Core Java
Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap.

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   Like         Discuss         Correct / Improve     java   collections   hashmap   map   concurrenthashmap   concurrenthashmap  concurrency   general electric   ge     Asked in 32 Companies        rare


  Q5. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.
Core Java
Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts  diamond problem     Asked in 20 Companies      basic        frequent


 Q6. What is the use of Synchronized block ?Core Java
Ans. The goal of a synchronised block is to achieve mutual exclusion i.e at one time, the segment of the code should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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   Like         Discuss         Correct / Improve     synchronized block   synchronized   synchronization   multithreading   threads   mutual exclusion   concurrency     Asked in 4 Companies      intermediate        frequent

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  Q7. How is multiple inheritance implemented in Java ?Core Java
Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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   Like         Discuss         Correct / Improve     multiple inheritance  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts   oops concept     Asked in 10 Companies        frequent


 Q8. How to Change Default Boot Kernel in Linux ?Unix
Ans. https://www.redhat.com/archives/rhl-list/2005-April/msg04167.html

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   Like         Discuss         Correct / Improve     unix  change default kernel     Asked in 1 Companies


 Q9. Difference between concurrentHashMap and HashTable ?Core Java
Ans. HashTable locks the complete collection to provide synchronization whereas ConcurrentHashMap only locks segments to achieve synchronization and hence better efficient and faster.

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   Like         Discuss         Correct / Improve     concurrentHashMap  HashTable  Map  Collections     Asked in 2 Companies



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