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Mobileum Gurgaon Interview Questions Answers

This is for Big Data Analytics(BDA team) in java

Is single thread useful on single core ?
two synchronized function on same instance can be accessed by 2 threads at the same time ?
Singleton,Factory and Observer design pattern
difference in java and c++ ?
are there global variables in java ?
any java profiler ?
how you debug out of memory in java ?
probable causes of out of memory in java ?
critical section ?
how achieve critical section in java ?
serialization and deserialization ? why ? how ? apis ? jackson
Garbage collector in java ? its lifecyce ?
store and retrieve 1 billion objects in java ? O(1) and most optimized memory ?
hashmap and equals ?
is hashmap threadsafe ?Concurrent HashMap
who takes care of fragmentation in java ?
is thread dump useful ?

cross multiply n matrices :
{1,2,3} {4,5} {6,7,8,9} … ——-> {1_4_6, 1_4_7,1_4_8 , 1_4_9 , 2_4_6 , 2_4_7 , 2_4_8}

Write a wrapper class over hashmap to make it thread safe ?

difference between notify and notifyall ?

Singleton class ? What happens if singleton class is loaded in multiple class loaders ?

Find min length in which a set of words exist in the given set of words ?

main(){
Student s = new Student(“tarun”,123,new Marks(1,2,3));
}
What is allocated and what remians at the end of execution of main memory ?

How many threads you shoould allocate if there are many jobs to complete including three io jobs , 3 cpu ?

How would you sort billions of 3 digit , 4 digit and 5 numbers with limited ram ?
Hint : use hashmaps for 3 digit , 4 digit and 5 digit numbers as key and then write them serially in file.

How would you represent 1 billion numbers if memory space is less than 1 billion bits ?
Hint:
In this case accuracy can be compromised to some extent and Heuristics would be used.