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

Interview Questions and Answers for 'Time' - 29 question(s) found - Order By Newest

Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback ) and Epam Systems

Q1. Difference between == and .equals() ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

Sample Code for equals

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Q2. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Core Java

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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Q3. What are points to consider in terms of access modifier when we are overriding any method?

Core Java

Ans. 1. Overriding method can not be more restrictive than the overridden method.

reason : in case of polymorphism , at object creation jvm look for actual runtime object. jvm does not look for reference type and while calling methods it look for overridden method.

If by means subclass were allowed to change the access modifier on the overriding method, then suddenly at runtime when the JVM invokes the true objects version of the method rather than the reference types version then it will be problematic

2. In case of subclass and superclass define in different package, we can override only those method which have public or protected access.

3. We can not override any private method because private methods can not be inherited and if method can not be inherited then method can not be overridden.

Sample Code for Overriding

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Basic and Very Frequently asked.

Q4. What is Polymorphism in Java ?

Core Java

Ans. Polymorphism means the condition of occurring in several different forms.

Polymorphism in Java is achieved in two manners

1. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas

2. Dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

Sample Code for overloading

Sample Code for overriding

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Almost sure to be asked in every company using any Dependency Injection framework ( Spring, Guice etc )

Q5. What is Dependency Injection or IOC ( Inversion of Control ) ?

Design

Ans. It is a Design Pattern that facilitates loose coupling by sending the dependency information ( object references of dependent object ) while building the state of the object. Objects are designed in a manner where they receive instances of the objects from other pieces of code, instead of constructing them internally and hence provide better flexibility.

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Very frequently asked.Usually among first few questions.

Q6. What is MVC ?

Design

Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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Q7. How Java provide high Performance ?

Core Java

Ans. Java uses Just-In-Time compiler to enable high performance. Just-In-Time compiler is a program that turns Java bytecode into instructions that can be sent directly to the processor.

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Usually asked to entry level software developers.

Q8. Write a program to swap two variables without using third

Core Java

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q9. If everything is an object , Cant we declare every object as

Object obj = new String();

Core Java

Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.

We cannot access methods defined in String class or in any class in hierarchy between String and Object.

For example - we cannot do obj.append("abc") as it will now give compile time error.

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Frequently asked to fresh graduates.

Q10. What is the difference between yield() and sleep()?

Operating System

Ans. When a object invokes yield() it returns to ready state. But when an object invokes sleep() method enters to not ready state.

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Q11. Name few tools for probing Java Memory Leaks ?

Ans. JProbe, OptimizeIt

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Q12. What are the sub classes of Exception class?

Core Java

Ans. The Exception class has two main subclasses : IOException class and RuntimeException Class.

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Q13. Name few Date and Time Classes you have used in your projects ?

Ans. http://www.buggybread.com/2015/02/java-util-date-time-classes-and.html

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Q14. In which cases isn't instanceof operator a bad practice?

Core Java

Ans. To avoid ClassCastException.

Though the following code will compile fine but will result in ClassCastException during runtime.

Fruit fruit = new Apple();
Banana banana = Banana(fruit); // ClassCastException

This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception.

This exception can be avoided by following code.

Fruit fruit = new Apple();
if(fruit instanceOf Banana){
Banana banana = Banana(fruit); // ClassCastException
}

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Q15. When are static and instance methods resolved ? During compile time or Runtime ?

Ans. Static methods are resolved during compile time and hence they cannot participate in runtime polymorphism. Instance methods are resolved during runtime.

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Q16. Which of the following do you think is the primary reason you would never use a static class even the application doesn't need multiple requests or threads ?

a. Serialization
b. Runtime Polymorphism
c. Lazy Loading
d. Memory

Ans. Runtime Polymorphism

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Q17. What is the use of Runtime Class ?

Ans. This class is used to provide access to the Java runtime system

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Q18. What is the difference between following time formats ?

hh:mm:ss
HH:mm:ss
kk:mm:ss
KK:mm:ss

Core Java

Ans. hh= hours in 1-12 format
HH= hours in 0-23 format
kk = Hours in 1-24 format
KK= hours in 0-11 format

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Q19. What is the difference between TimeBasedRollingPolicy and SizeBasedTriggeringPolicy within Log4j ? Can we use both together and What would that mean ?

Log4j

Ans. TimeBasedRollingPolicy enables rolling of logs based on the time / days whereas SizeBasedTriggeringPolicy enables rolling of logs based on size cap.

Yes we can use both together. In that case Logs will be rolled in case any of the condition is met i.e after the interval or if the size is reached.

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Q20. What is "dynamic method dispatch" in java ?

Core Java

Ans. dynamic method dispatch is a process in which a call to an
overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java.

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Q21. What is dynamic dispatch in Java ?

Core Java

Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime.

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Q22. What is the difference between latency, response time and processing time ?

Web Service

Ans. Latency is the delay incurred while communicating a message i.e the time took the message in transit over network.

processing time is the delay it took for the server to process the request.

Response time is the sum total of latency and processing time.

For example -

Let's say it takes 1 ms for the request to reach from client to server and similar 1 ms for the response to come back to client. Moreover it takes approx 10 ms for the application to process the request. So The response time would be outward latency + processing time + inward latency = 12 ms

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Q23. What is the default data type of Serialized methods?'

Core Java

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

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Q24. How would you design a stack which, in addition to push and pop, also has a function min which returns the minimum element? Push, pop and min should all operate in O(1) time

Algorithm

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Q25. Is Runtime Polymorphism possible without Inheritance ?

Core Java

Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation.

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Q26. What is virtual table with respect to method overriding in Java ?

Core Java

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Q27. How is the virtual method table implemented in Java?

Core Java

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Q28. How many VTables are there for each class ?

Core Java

Ans. There is one VTable for each class.

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Q29. What is Time slicing with respect to Threads ?

Operating System

Ans. Time Slicing is the process to divide the available CPU time to the available runnable threads.

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Q30. Runtime Polymorphism in Java is achieved through ..

Core Java

a. Method Overloading

b. Method Overriding

c. Variable Overloading

d. Variable Overriding

Ans.b. Method Overriding

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