Core Java - Interview Questions and Answers for 'Basic interview question' | Search Java Interview Question

Core Java - Interview Questions and Answers for 'Basic interview question' - 39 question(s) found - Order By Newest

Very frequently asked to Fresh graduates.

Q1. What is the difference between Encapsulation and Abstraction?

Core Java

^Anonymous

Ans. 1.Abstraction solves the problem at design level while encapsulation solves the problem at implementation level

2.Abstraction is used for hiding the unwanted data and giving relevant data. while Encapsulation means hiding the code and data into a single unit to protect the data from outside world.

3. Abstraction lets you focus on what the object does instead of how it does it while Encapsulation means hiding the internal details or mechanics of how an object does something.

4.For example: Outer Look of a Television, like it has a display screen and channel buttons to change channel it explains Abstraction but Inner Implementation detail of a Television how CRT and Display Screen are connect with each other using different circuits , it explains Encapsulation.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops oops concepts encapsulation object oriented programming (oops) oops concepts abstraction basic interview question Asked in 10 Companies basic frequent}

Try 2 Question(s) Test

Very frequently asked across all types of companies.

Q2. Difference between HashMap and Hashtable?

Core Java

^Anonymous

Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections hashmap map hashtable basic interview question ebay tcs hcl technologies infosys technologies Asked in 14 Companies basic frequent}

Try 2 Question(s) Test

Very Frequently asked to fresh graduates and less experienced. Favorite question in Walk in drives. Frequently asked in Indian Services companies.

Q3. Difference between Overloading and Overriding ?

Core Java

^Anonymous

Ans. Overloading - Similar Signature but different definition , like function overloading.

Overriding - Overriding the Definition of base class in the derived class.

Sample Code for overloading

Sample Code for overriding

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops overloading overriding oops concepts basic interview question Asked in 83 Companies basic frequent}

Try 1 Question(s) Test

Very Frequently asked across all type of companies and across all levels.

Q4. Difference between Public, Private, Default and Protected ?

Core Java

^Anonymous

Ans. Private - Not accessible outside object scope.

Public - Accessible from anywhere.

Default - Accessible from anywhere within same package.

Protected - Accessible from object and the sub class objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oop access specifier public private default protected basic interview question Asked in 11 Companies basic frequent}

Try 1 Question(s) Test

Q5. What is casting?

Core Java

^Anonymous

Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java data types casting type casting basic interview question Asked in 8 Companies basic frequent}

Frequently asked to fresh graduates and less experienced.

Q6. Difference between Composition and Inheritance ?

Core Java

^{Admin
info@buggybread.com}

Ans. Inheritance means a object inheriting reusable properties of the base class. Compositions means that an abject holds other objects.

In Inheritance there is only one object in memory ( derived object ) whereas in Composition , parent object holds references of all composed objects.

From Design perspective - Inheritance is "is a" relationship among objects whereas Composition is "has a" relationship among objects.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops oops concepts inheritance object oriented programming (oops) oops concepts composition object oriented programming (oops) oops concepts difference between basic interview question Asked in 12 Companies basic frequent}

Try 2 Question(s) Test

Q7. Does Java support Multiple Inheritance ?

Core Java

^Anonymous

Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oop oop concepts inheritence multiple inheritence basic interview question Asked in 10 Companies basic frequent}

Try 1 Question(s) Test

Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.

Q8. What is a Final Variable ?

Core Java

^Anonymous

Ans. Final variable is a variable constant that cannot be changed after initialization.

Sample Code for final variable

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve oops java final final variable basic interview question Asked in 12 Companies basic frequent}

Try 1 Question(s) Test

Q9. Difference between Abstract and Concrete Class ?

Core Java

^Anonymous

Ans. Abstract classes are only meant to be sub classed and not meant to be instantiated whereas concrete classes are meant to be instantiated.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops abstract classes basic interview question Asked in 1 Companies basic frequent}

Q10. Difference between Vector and ArrayList ?

Core Java

^Anonymous

Ans. Vectors are synchronized whereas Array lists are not.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java basic interview question vector arraylist collections synchronization Asked in 34 Companies basic frequent}

Frequently asked to fresh graduates.

Q11. Explain Thread States ?

Operating System

^{Admin
info@buggybread.com}

Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities.

Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn.

Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish.

Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method.

Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes.

Blocked on synchronization - Will move to Runnable when a lock is acquired.

Dead - The thread is finished working.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading scheduling thread states basic interview question Asked in 1 Companies basic frequent}

Try 2 Question(s) Test

Q12. What is a Final Method ?

Core Java

^Anonymous

Ans. A Method that cannot be overriden in the sub class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops java keywords final final method overriding basic interview question basic frequent}

Try 1 Question(s) Test

Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.

Q13. What is a Final Class ?

^Anonymous

Ans. A Class that cannot be sub classed.

Sample Code for final class

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops final final class java keyword basic interview question Asked in 3 Companies basic frequent}

Very Frequently asked. Usually asked along with String Class related questions.

Q14. What is an immutable class ?

Core Java

^Anonymous

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops immutable immutability immutable immutability class string class basic interview question Asked in 18 Companies Basic frequent}

Try 2 Question(s) Test

Q15. Name few Java Exceptions ?

Core Java

^Anonymous

Ans. IndexOutofBoundException ,
NoClassDefFoundException ,
OutOfMemoryException ,
IllegalArgumentException,
NullPointerException,
IllegalStateException

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops exceptions basic interview question basic frequent}

Q16. What is "super" used for ?

^Anonymous

Ans. Used to access members of the base class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops java keywords super basic interview question Asked in 2 Companies basic frequent}

Q17. What is "this" keyword used for ?

^Anonymous

Ans. Used to represent an instance of the class in which it appears.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops java keywords this basic interview question basic frequent}

Frequently asked to fresh graduates.

Q18. Difference between Process and Thread ?

Operating System

^Anonymous

Ans. Process is a program in execution whereas thread is a separate path of execution in a program.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java threads multi threading operating system basic interview question Asked in 24 Companies basic frequent}

Q19. What is an Enum type ?

Core Java

^Anonymous

Ans. An enum type is a special data type that enables for a variable to be a set of predefined constants

Sample Code for enum

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java java5 enum basic interview question basic frequent}

Try 2 Question(s) Test

Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.

Q20. Difference between StringBuffer and StringBuilder ?

Core Java

^Anonymous

Ans. StringBuffer is synchronized whereas StringBuilder is not.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java string stringbuffer string class stringbuilder synchronized basic interview question infosys technologies Asked in 17 Companies basic frequent}

Try 1 Question(s) Test

Q21. Difference between nested and inner classes ?

^Anonymous

Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops static nested classes inner classes basic interview question basic frequent}

Try 1 Question(s) Test

Q22. What is the difference between float and double?

^{Admin
info@buggybread.com}

Ans. Float can represent up to 7 digits accurately after decimal point, where as double can represent up to 15 digits accurately after decimal point.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java data types float double difference between basic interview question}

Q23. What are the features of encapsulation ?

Core Java

^{Admin
info@buggybread.com}

Ans. Combine the data of our application and its manipulation at one place.

Encapsulation Allow the state of an object to be accessed and modified through behaviors.

Reduce the coupling of modules and increase the cohesion inside them.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops oops concepts encapsulation object oriented programming (oops) oops concepts basic interview question Asked in 2 Companies basic frequent}

Frequently asked at HCL Technologies ( Based on 3 feedback )

Q24. Difference between Checked and Unchecked exceptions ?

Core Java

^Anonymous

Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java exceptions checked exceptions unchecked exceptions exception handling basic interview question Asked in 37 Companies basic frequent}

Try 1 Question(s) Test

Q25. What is a finalize method ?

Core Java

^Anonymous

Ans. finalize() method is called just before an object is destroyed.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops finalize garbage collection basic interview question Asked in 1 Companies basic frequent}

Try 1 Question(s) Test

Q26. Can we overload constructors ?

^Anonymous

Ans. Yes.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops constructors overloading yes-no basic interview question}

Q27. what is the difference between collections class vs collections interface ?

Core Java

^{Admin
info@buggybread.com}

Ans. Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections collections class collection interface basic interview question Asked in 6 Companies basic frequent}

Try 1 Question(s) Test

Q28. What is the advantage of using arrays over variables ?

^{Admin
info@buggybread.com}

Ans. Arrays provide a structure wherein multiple values can be accessed using single reference and index. This helps in iterating over the values using loops.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java arrays loops variables basic interview question}

Q29. Advantage of Collection classes over Arrays ?

Core Java

^{Admin
info@buggybread.com}

Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment.
Collections can hold both homogeneous and heterogeneous data's.
Every collection follows some standard data structures.
Collection provides many useful built in methods for traversing,sorting and search.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections collections classes advantages of collections over arrays collections vs arrays basic interview question Asked in 6 Companies basic frequent}

Q30. What is the difference between System.out ,System.err and System.in?

^{Admin
info@buggybread.com}

Ans. System.out and System.err both represent the monitor by default and hence can be used to send data or results to the monitor. But System.out is used to display normal messages and results whereas System.err is used to display error messages and System.in represents InputStream object, which by default represents standard input device, i.e., keyboard.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java io system.out system.err system.in difference between advanced basic interview question}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.