Rarely asked Interview Questions and Answers

Rarely asked Interview Questions and Answers - 72 question(s) found - Order By Rating

Q1. Explain Transitive equals contract.

Ans. The equals contract is said to be transitive if

obj1.equals(obj2); and obj2(.equals(obj3)

then obj1.equals(obj3) also returns true.

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Q2. Have you ever used java.util.Objects class ?

Core Java

Ans. Yes, We are using requireNonNull method for validating if the object is null.

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Q3. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q4. How is the virtual method table implemented in Java?

Core Java

^{This question is still unanswered. Can you please provide an answer.}

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Q5. What is MVC in GUI components ?

Design

Ans. The Model/View/Controller pattern, a strategy for dividing responsibility in a GUI component.

The model is the data for the component.

The view is the visual presentation of the component on the screen.

The controller is responsible for reacting to events by changing the model.

According to the MVC pattern, these responsibilities should be handled by different objects.

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Q6. What value you would like to see in an employee if you own a company ?

General

Ans. The intent of this question is to see what values as a employee you have. So answer this cautiously as they will try to judge you on the basis of this answer.

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Q7. What is the difference between TreeSet and TreeMap ?

Core Java

Ans. TreeSet contains only values as elements whereas TreeMap contains Key value pairs.

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Q8. How Bitly shortens the URL ?

Web

^{This question was recently asked at 'Symantec'.This question is still unanswered. Can you please provide an answer.}

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Q9. What is a weak reference ?

Core Java

Ans. A weak reference is a reference that gets removed on the next garbage collection cycle.

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Q10. What is an applet ?

Java EE

^{This question was recently asked at 'American International Group (AIG)'.This question is still unanswered. Can you please provide an answer.}

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Q11. 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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Q12. Why can we have a static inner class but not a static Top level class in Java ?

Core Java

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Q13. How does making string as immutable helps with securing information ? How does String Pool pose a security threat ?

Core Java

Ans. String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment or hacker over internet.

Once a String constant is created in Java , it stays in string constant pool until garbage collected and hence stays there much longer than what's needed. Any unauthorized access to string Pool pose a threat of exposing these values.

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Q14. How Marker interfaces works internally ?

Core Java

^{This question was recently asked at 'GGK Technologies'.This question is still unanswered. Can you please provide an answer.}

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Q15. What is Exception Wrapping ?

Ans. Exception wrapping is wrapping an exception object within another exception object and then throwing the outer exception.

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Q16. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Core Java

Ans. First will not create physical file in storage whereas the second will.

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Q17. Which memory segment holds String Pool in Java ?

Core Java

Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

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Q18. How does Java handle integer overflows and underflows?

Core Java

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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Q19. Is there a way to know size of an object in Java ?

Core Java

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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Q20. Can we declare static variables as transient ?

Core Java

Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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Q21. What is serialVersionUID ?

Core Java

Ans. Everytime an object is serialized the java serialization mechanism automatically computes a hash value by passing the meta information for the class. This id is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization

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Q22. Can you write a "Hello World" program without using any ";" within it?

Core Java

Ans. Yes, That is possible

class A {
public static void main(String args[]){
if(System.out.printf("Hello World")==null){}
}
}

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Q23. Write a Program to check if 2 strings are Anagrams ?

Core Java

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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Q24. How can we catch an exception thrown by another thread ?

Core Java

Ans. http://stackoverflow.com/a/6548203/2789764

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Q25. How can we find the memory usage of JVM from Java code?

Core Java

Ans. Using Runtime object.

Runtime runtime = Runtime.getRuntime();

runtime.totalMemory();
runtime.freeMemory();

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Q26. Is ++ or -- operation thread safe in Java ?

Core Java

Ans. No

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Q27. How can one determine if JVM is 32-bit or 64-bit from Java Program ?

Core Java

Ans. There is a Java system property "sun.arch.data.model" that can tell if JVM is 32 bit of 64 bit

System.getProperty("sun.arch.data.model") can be used to get that property.

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Usually asked with Questions related to Generics.

Q28. What are Type Erasures in Java ?

Core Java

Ans. Type erasure applies to the use of generics. When generics are used, they're pre compiled into compile time checks and execution-time casts.

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Q29. Have you heard about the external table feature of Oracle ?

Database

Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems.

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Q30. What happens to the Exception object after the exception handling is done ?

Core Java

Ans. As with all other objects its garbage collected after its usage unless its rethrown.

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