interview questions (java developer) | Questions & Answers (100 %Score) Latest Updated
2024/2025 Comprehensive Questions A+ Graded Answers | With Expert Solutions
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.
What is the static keyword. give examples. - Can declare a static class within a class.
Memory for all static variables will be allocated and this will be done only once
static methods can be called from any where by
calling the class ex: Class.staticMethod()
1. Given Employee Class . How can you sort out the data available in a list of employees.
2. Given Employee Class with age . How can you sort out the data by age . - implementing Comparable
on the Employee class and overriding compareTo method
then Collections.sort(employeeList) will sort employees.
Create a new class called EmployeeAgeComparator implementing comparator , then overriding compare
method .
using Collections.sort(employeeList, employeeAgeComparator) will sort the list by age.
What are generics ? - Customize class or methods to whatever type you are working with.
Can use T to return the object
2024/2025 Comprehensive Questions A+ Graded Answers | With Expert Solutions
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.
What is the static keyword. give examples. - Can declare a static class within a class.
Memory for all static variables will be allocated and this will be done only once
static methods can be called from any where by
calling the class ex: Class.staticMethod()
1. Given Employee Class . How can you sort out the data available in a list of employees.
2. Given Employee Class with age . How can you sort out the data by age . - implementing Comparable
on the Employee class and overriding compareTo method
then Collections.sort(employeeList) will sort employees.
Create a new class called EmployeeAgeComparator implementing comparator , then overriding compare
method .
using Collections.sort(employeeList, employeeAgeComparator) will sort the list by age.
What are generics ? - Customize class or methods to whatever type you are working with.
Can use T to return the object
