Java Interview Review Questions and Answers (100% Pass)
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."
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