interview questions java
developer Questions and
Answers
What is a immutable class?
✓~ A defined class where state of the object cannot be modified.
What is the default sorting order in TreeMap?
✓~ Natural Ordering
What is the difference between wait() and sleep()
✓~ wait is from the object class, used from synchronized object block until lock is acquired
. Simply used for thread synchronization.
sleep is from thread class. Used for adding a delay/pause to a thread, throws
InterruptedException.
What are the bean scopes available in spring ? explain each scope.
,✓~ Singleton: By default spring creates a singleton bean. One bean instance used
throughout the application.
Prototype: Used to create a bean every time its needed.
Request: Used for Spring web aware context, each request that is made has its own
instance of a bean.
Session: Used for Spring web aware context, bean instantiated bases on session
scope lives throughout http Session.
Global Session: Used for spring web aware context and its defined for only portlet
application.
What is cascade delete.
✓~ When a parent row is deleted the child row should also be deleted in the database.
JAVA OOP Design Principles ? Explain Each
✓~ Encapsulation: Used to hide classes/ variables and behavior from other classes.
,Abstraction: Is a concrete class to only show certain features of the class. Can use
the abstract keyword to create abstract class. Contains abstract methods and non
abstract methods.
Inheritance: Can inherit properties / behaviors of the parent class by using the
extend keyword.
Polymorphism: I used to take a form of an object of another.
What design patterns have you worked on?
✓~ IOC -singleton
Factory
Adapter/connector
How do you implement a singleton class in java (without spring) and in java (with
spring)
✓~ Java (without spring) : have a class and make the constructor private. Create a static
method for you to get the returned instance of it.
java (with spring) : Annotate the class with @component or @service .. etc. and the
IOC container will create the bean in a default singleton scope.
, What is the volatile keyword?
✓~ It is enclosed within a synchronized block.
Thread A is accessing the volatile variable so thread B cannot access it.
This variable is read from the main memory and it does not cache it.
How do you create a immutable class ?
✓~ Declare the class as final
Declare instance variables as final
do not contain any setter.
What is the final key word. give examples for class , variable, and methods.
✓~ on class level, another class cannot extend to the final class.
on variables, variables are defined as constant. cannot be changed.
method variables as final cannot be overridden by another class.
developer Questions and
Answers
What is a immutable class?
✓~ A defined class where state of the object cannot be modified.
What is the default sorting order in TreeMap?
✓~ Natural Ordering
What is the difference between wait() and sleep()
✓~ wait is from the object class, used from synchronized object block until lock is acquired
. Simply used for thread synchronization.
sleep is from thread class. Used for adding a delay/pause to a thread, throws
InterruptedException.
What are the bean scopes available in spring ? explain each scope.
,✓~ Singleton: By default spring creates a singleton bean. One bean instance used
throughout the application.
Prototype: Used to create a bean every time its needed.
Request: Used for Spring web aware context, each request that is made has its own
instance of a bean.
Session: Used for Spring web aware context, bean instantiated bases on session
scope lives throughout http Session.
Global Session: Used for spring web aware context and its defined for only portlet
application.
What is cascade delete.
✓~ When a parent row is deleted the child row should also be deleted in the database.
JAVA OOP Design Principles ? Explain Each
✓~ Encapsulation: Used to hide classes/ variables and behavior from other classes.
,Abstraction: Is a concrete class to only show certain features of the class. Can use
the abstract keyword to create abstract class. Contains abstract methods and non
abstract methods.
Inheritance: Can inherit properties / behaviors of the parent class by using the
extend keyword.
Polymorphism: I used to take a form of an object of another.
What design patterns have you worked on?
✓~ IOC -singleton
Factory
Adapter/connector
How do you implement a singleton class in java (without spring) and in java (with
spring)
✓~ Java (without spring) : have a class and make the constructor private. Create a static
method for you to get the returned instance of it.
java (with spring) : Annotate the class with @component or @service .. etc. and the
IOC container will create the bean in a default singleton scope.
, What is the volatile keyword?
✓~ It is enclosed within a synchronized block.
Thread A is accessing the volatile variable so thread B cannot access it.
This variable is read from the main memory and it does not cache it.
How do you create a immutable class ?
✓~ Declare the class as final
Declare instance variables as final
do not contain any setter.
What is the final key word. give examples for class , variable, and methods.
✓~ on class level, another class cannot extend to the final class.
on variables, variables are defined as constant. cannot be changed.
method variables as final cannot be overridden by another class.
