interview questions java developer Questions and Answers
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Course
Java developer
Institution
Java Developer
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 ac...
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.
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