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

Interview Questions and Answers - Order By Newest

Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )

Q11. What are different ways of object creation in Java ?

Ans. Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method - (Class.forName(xyzClass))emp.newInstance( )

By cloning an already available object - (xyzClass)obj1.clone( )

Sample Code for object initialization using clone

Sample Code for object initialization using getInstance

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

_{Like Discuss Correct / Improve java oops object creation new operator class.forname cloning ebay Asked in 9 Companies expert}

Very Frequently asked. Have been asked in HCL Technologies very frequently ( based on 3 feedback ). Among first few questions in many interviews.

Q12. Differences between abstract class and interface ?

Core Java

Ans. Abstract classes can have both abstract methods ( method declarations ) as well as concrete methods ( inherited to the derived classes ) whereas Interfaces can only have abstract methods ( method declarations ).

A class can extend single abstract class whereas it can implement multiple interfaces.

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

_{Like Discuss Correct / Improve java classes abstract class interfaces abstract class vs interface abstract classes vs interfaces Asked in 82 Companies basic frequent}

Frequently asked in Infosys India

Q13. What is a String Pool ?

Core Java

Ans. String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

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

_{Like Discuss Correct / Improve java oops string string class string pool heap memory Asked in 31 Companies intermediate frequent}

Try 2 Question(s) Test

Q14. What are different types of classes ?

Core Java

Ans. There are different verticals in which Java Classes can be classified.

1. Access - Public , Private , default or Protected.

2. Packaging - System, library or User Defined

3. Structure - Outer or Inner

4. Object Derivation - Abstract Class or Concrete Class.

5. Object Creation - Normal, Singleton , Doubleton , Immutable or Enum.

6. Functionality - String , Util , Stream etc.

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

_{Like Discuss Correct / Improve classes different types of classes Asked in 1 Companies}

Try 1 Question(s) Test

Q15. Can you give a real world example of Encapsulation and Abstraction ?

Core Java

Ans. Car Engine is an example of encapsulation and abstraction. You ignite the car using an interface called starter and least bothered about how the tire actually moves (This is abstraction). The engine encapsulates the complete process to itself only and doesn't allow you to start the other components like the radiator etc ( this is excapsulation )

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

_{Like Discuss Correct / Improve encapsulation object oriented programming (oops) oops concepts abstraction oops oops features java features Asked in 13 Companies}

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

Q16. What are the methods of Object Class ?

Core Java

Ans. clone() - Creates and returns a copy of this object.

equals() - Indicates whether some other object is "equal to" this one.

finalize() - Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

getClass() - Returns the runtime class of an object.

hashCode() - Returns a hash code value for the object.

toString() - Returns a string representation of the object.

notify(), notifyAll(), and wait() - Play a part in synchronizing the activities of independently running threads in a program.

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

_{Like Discuss Correct / Improve java oops object class Asked in 16 Companies basic frequent}

Try 1 Question(s) Test

Q17. Difference between Static and Singleton Class ?

Core Java

Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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

_{Like Discuss Correct / Improve Static Class Singleton Static Class vs Singleton Asked in 3 Companies Intermediate frequent}

Very frequently asked in companies using SOA.

Q18. What are RESTful Web Services ?

Rest

Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -

1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.

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

_{Like Discuss Correct / Improve java web services rest java j2ee architecture Asked in 14 Companies intermediate frequent}

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

Q19. 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.

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

_{Like Discuss Correct / Improve design patterns ioc ( Inversion of Control ) dependency injection Asked in 83 Companies intermediate frequent}

Q20. Which of the following are valid declarations

1. void method(int... x){};
2. void method(int.. x){};
3. void method(int.. .x){};
4. void method(int ...x){};
5. void method(int... x){};
6. void method(int ... x){};
7. void method(int x, int... y){};
8. void method(int... x, int y){};
9. void method(int... x,int... y){};

Core Java

Ans. 1st is a valid and standard declaration.

2nd results in compilation error as only 2 dots are there.

3rd results in compilation error as three dots are not consecutive and broken.

4 through 6 may not be standard and ideal way of declarations but they are valid and will compile and work fine.

7 is valid declaration.

8 and 9 will result in compilation error as var args can only be provided to last argument.

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

_{Like Discuss Correct / Improve var args methods functions method declaration scjp ocjp}

Q21. What will this code print ?

String a = new String ("TEST");
String b = new String ("TEST");
if(a == b) {
System.out.println ("TRUE");
} else {
System.out.println ("FALSE");
}

Core Java

Ans. FALSE. == operator compares object references, a and b are references to two different objects, hence the FALSE. .equals method is used to compare string object content.

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

_{Like Discuss Correct / Improve string string class java == object references coding Asked in 2 Companies basic frequent}

Try 1 Question(s) Test

Q22. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");

Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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

_{Like Discuss Correct / Improve java collections arraylist list autoboxing wrapper classes expert rare}

Advanced level question. Recently asked in few Indian service companies ( Based on 3 inputs )

Q23. What are various types of Class loaders used by JVM ?

Core Java

Ans. Bootstrap - Loads JDK internal classes, java.* packages.

Extensions - Loads jar files from JDK extensions directory - usually lib/ext directory of the JRE

System - Loads classes from system classpath.

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

_{Like Discuss Correct / Improve java jvm memory management class loaders bootstrap extensions system classloaders advanced technical lead technical architect Asked in 7 Companies}

Q24. Which access specifiers can be used with top level class ? a. public or default b. public or private c. public or protected d. protected or default

Core Java

Ans. public or default

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

_{Like Discuss Correct / Improve access specifier oops java class Asked in 2 Companies}

Q25. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes

Core Java

Ans. Methods , Variables , Initialization Blocks and nested Classes

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

_{Like Discuss Correct / Improve oops java static nested classes static nested classes}

Try 2 Question(s) Test

Q26. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();

Core Java

Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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

_{Like Discuss Correct / Improve inner classes inner class static inner class new operator}

Q27. What is JUnitRunner ?

JUnit

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

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

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q28. What are the Wrapper classes available for primitive types ?

Core Java

Ans. boolean - java.lang.Boolean
byte - java.lang.Byte
char - java.lang.Character
double - java.lang.Double
float - java.lang.Float
int - java.lang.Integer
long - java.lang.Long
short - java.lang.Short
void - java.lang.Void

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

_{Like Discuss Correct / Improve java java5 data types wrapper classes adapter design pattern rare}

Q29. Which String class does not override the equals() and hashCode() methods, inheriting them directly from class Object?

Core Java

Ans. java.lang.StringBuffer.

Sample Code for StringBuffer

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

_{Like Discuss Correct / Improve java object class stringbuffer expert rare}

Q30. What are wrapper classes ?

Core Java

Ans. They are wrappers to primitive data types. They allow us to access primitives as objects.

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

_{Like Discuss Correct / Improve java data types wrapper classes Asked in 3 Companies basic frequent}

Q31. How to implement an immutable class ?

Core Java

Ans. We can make a class immutable by

1. Making all methods and variables as private.

2. Setting variables within constructor.

Public Class ImmutableClass{

private int member;
ImmutableClass(int var){
member=var;
}
}

and then we can initialize the object of the class as

ImmutableClass immutableObject = new ImmutableClass(5);

Now all members being private , you cant change the state of the object.

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 technical lead Asked in 5 Companies intermediate frequent}

Try 2 Question(s) Test

Q32. What are the contents of Hibernate configuration file ( hibernate.cfg.xml ) ?

Hibernate

Ans. HBM Files ( Mapping )
DB Connection ( DB Connection String , User Name , Password , Pool Size )
SQL Dialect ( SQL variant to be generated )
Show SQL ( Show / No show SQL on Console )
Auto Commit ( True / False )

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

_{Like Discuss Correct / Improve hibernate configuration barclays Asked in 11 Companies}

Q33. Why do we need Thread class even in case we execute thread using runnable interface ?

Core Java

Ans. Thread class holds the definition of start method ( This is the method that starts execution of new thread and then calls run method within the scope of new thread ). Interfaces don't hold any definition and so does runnable. So it makes it necessary the usage of Thread class , whatever implementation you choose.

When your class extends the thread class, it carries the definition of start method from parent Thread class onto itself and hence new yourClass.start() helps starting a new thread and then executing run method in that new thread scope.

When you implement runnable interface , you are just making it sure to the JVM that you have implemented the required method ( run() ) which the Thread start method will look for upon executing start method.

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

_{Like Discuss Correct / Improve java threads multithreading runnable interface thread class}

Q34. What is the difference between these two method declarations ?

private static void method(String[] arg)

and

private static void method(String... arg)

Core Java

Ans. First expects the argument as a string array whereas second expects variable number of string arguments or a string array.

So we can call both by providing string array as an argument but second can be called with 0 to n string arguments which cannot be done for first.

for example - We can call second method with any of following

method();
method("Hello");
method("Hello","World");
method(new String[4]);

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

_{Like Discuss Correct / Improve var args methods method declarations functions}

Q35. What is the difference between inner class and sub class ?

Core Java

Ans. Inner Class is a class that is nested within another class whereas sub class is a class that extends or inherit another class.

Inner class can only be accessed using reference of outer class ( Class name , if inner class is static or object reference, if inner class is non static ) whereas Sub class is accessed directly.

In terms of memory, inner class is stored just like another class having it's own body whereas sub class carries the body of parent class as well as it's own fields in memory.

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

_{Like Discuss Correct / Improve inner classes nested classes inner class vs sub class nested class vs sub class Basic}

Q36. What are the benefits of using Wrapper classes over primitive types ?

Core Java

Ans. With Collection classes , we cannot use primitive types. Moreover for any class using generic types, we cannot use primitive types.

They add more functionality by means of additional methods.

As their reference can be null , they offer consistent check for uninitialized state.

They facilitate caching and reuse by means of constant Pools.

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

_{Like Discuss Correct / Improve wrapper classes benefits of wrapper classes over primitives}

Q37. What are the different types of inner classes ?

Core Java

Ans. Simple Inner Class,
Local Inner Class,
Anonymous Inner Class,
Static Nested Inner Class.

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

_{Like Discuss Correct / Improve java inner classes classes Asked in 6 Companies basic frequent}

Try 1 Question(s) Test

Frequently asked at HCL Technologies ( Based on 3 feedback )

Q38. Difference between Checked and Unchecked exceptions ?

Core Java

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 checked vs unchecked exceptions Asked in 39 Companies basic frequent}

Try 1 Question(s) Test

Q39. Difference between Abstract and Concrete Class ?

Core Java

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 Abstract vs Concrete Class Asked in 1 Companies basic frequent}

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

Q40. What is an immutable class ?

Core Java

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

Search Interview Questions

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