Java Interview Review | Questions & Answers (100 %Score) Latest Updated 2024/2025
Comprehensive Questions A+ Graded Answers | With Expert Solutions
What is the difference between an Interface and an Abstract class? - "An abstract class can have
instance methods that implement a default behavior. An Interface can only declare constants and
instance methods, but cannot implement default behavior and all methods are implicitly abstract. An
interface has all public members and no implementation. An abstract class is a class which may have the
usual flavors of class members (private, protected, etc.), but has some abstract methods."
CRUD - " Create, Retrieve, Update, Delete"
"What is the technical name of the ""String"" part in the statement List<String>" - Generics
Extends vs Implements - "A Java class may implement, and an interface may extend, any number of
interfaces; however an interface may not implement an interface."
What is a singleton? - "A singleton class is a design pattern that only allows a single instanciated instance
of a class. You do this by making the constructor private and having a static method that ""getInstance""
that will be a pointer to a local copy. NOTE, in general it's NOT thread safe"
.equals vs == - The .equals compares values and the == compares references.
inner join vs left outer - An inline function is one for which the compiler copies the code from the
function definition directly into the code of the calling function rather than creating a separate set of
instructions in memory. Instead of transferring control to and from the fun
Write SQL that will group all countries that more than more city. - "select countryCode, count(*)
""COUNT"" from world.city group by countryCode having count > 2"
Difference between Vector and ArrayList? - Vector is synchronized whereas arraylist is not.
, application server - "An application server is a server which provides software applications with services
such as security, data services, transaction support, load balancing, and management of large
distributed systems"
What is OOP - "Object-oriented programming (OOP) is a programming paradigm using ""objects"" - data
structures consisting of data fields and methods together with their interactions - to design applications
and computer programs. There are three main principals of oops which are called Polymorphism,
Inheritance and Encapsulation. Other parts include data abstraction, messaging and modularity."
What is data abstraction? And what is it related to? - "OOP: abstraction is the process by which data and
programs are defined with a representation similar in form to its meaning (semantics), while hiding
away the implementation details. Abstraction tries to reduce and factor out details so that the
programmer can focus on a few concepts at a time"
What is encapsulation? And what is it related to? - OOP: A language mechanism for restricting access to
some of the object's components OR A language construct that facilitates the bundling of data with the
methods (or other functions) operating on that data
What is Ploymorphism? And what is it related to? - "OOP: the ability to create a variable, a function, or
an object that has more than one form"
What is Inheritance? And what is it related to? - "OOP: a way to reuse code of existing objects, establish
a subtype from an existing object, or both"
Describe MVC - "In software engineering, Model-View-Controller (MVC) is an architectural pattern that
splits interactions between users and applications into three roles: the Model (business logic), the View
(user interface), and the Controller (user input)"
Synchronization overview - "The Java programming language supports multiple threads, using a monitor
construction for synchronization. In the Java language, a method can be declared as synchronized. A
built-in mechanism ensures that only one Java thread can execute an object's synchronized methods at
a time. The mechanism also allows threads to wait for resources to become available, and allows a
thread that makes a resource available to notify other threads that are waiting for the resource. This
web page describes this mechanism and its use. But first, we need to look at an example that illustrates
why synchronization is needed."
Comprehensive Questions A+ Graded Answers | With Expert Solutions
What is the difference between an Interface and an Abstract class? - "An abstract class can have
instance methods that implement a default behavior. An Interface can only declare constants and
instance methods, but cannot implement default behavior and all methods are implicitly abstract. An
interface has all public members and no implementation. An abstract class is a class which may have the
usual flavors of class members (private, protected, etc.), but has some abstract methods."
CRUD - " Create, Retrieve, Update, Delete"
"What is the technical name of the ""String"" part in the statement List<String>" - Generics
Extends vs Implements - "A Java class may implement, and an interface may extend, any number of
interfaces; however an interface may not implement an interface."
What is a singleton? - "A singleton class is a design pattern that only allows a single instanciated instance
of a class. You do this by making the constructor private and having a static method that ""getInstance""
that will be a pointer to a local copy. NOTE, in general it's NOT thread safe"
.equals vs == - The .equals compares values and the == compares references.
inner join vs left outer - An inline function is one for which the compiler copies the code from the
function definition directly into the code of the calling function rather than creating a separate set of
instructions in memory. Instead of transferring control to and from the fun
Write SQL that will group all countries that more than more city. - "select countryCode, count(*)
""COUNT"" from world.city group by countryCode having count > 2"
Difference between Vector and ArrayList? - Vector is synchronized whereas arraylist is not.
, application server - "An application server is a server which provides software applications with services
such as security, data services, transaction support, load balancing, and management of large
distributed systems"
What is OOP - "Object-oriented programming (OOP) is a programming paradigm using ""objects"" - data
structures consisting of data fields and methods together with their interactions - to design applications
and computer programs. There are three main principals of oops which are called Polymorphism,
Inheritance and Encapsulation. Other parts include data abstraction, messaging and modularity."
What is data abstraction? And what is it related to? - "OOP: abstraction is the process by which data and
programs are defined with a representation similar in form to its meaning (semantics), while hiding
away the implementation details. Abstraction tries to reduce and factor out details so that the
programmer can focus on a few concepts at a time"
What is encapsulation? And what is it related to? - OOP: A language mechanism for restricting access to
some of the object's components OR A language construct that facilitates the bundling of data with the
methods (or other functions) operating on that data
What is Ploymorphism? And what is it related to? - "OOP: the ability to create a variable, a function, or
an object that has more than one form"
What is Inheritance? And what is it related to? - "OOP: a way to reuse code of existing objects, establish
a subtype from an existing object, or both"
Describe MVC - "In software engineering, Model-View-Controller (MVC) is an architectural pattern that
splits interactions between users and applications into three roles: the Model (business logic), the View
(user interface), and the Controller (user input)"
Synchronization overview - "The Java programming language supports multiple threads, using a monitor
construction for synchronization. In the Java language, a method can be declared as synchronized. A
built-in mechanism ensures that only one Java thread can execute an object's synchronized methods at
a time. The mechanism also allows threads to wait for resources to become available, and allows a
thread that makes a resource available to notify other threads that are waiting for the resource. This
web page describes this mechanism and its use. But first, we need to look at an example that illustrates
why synchronization is needed."
