Java Interview Review
Questions and Answers
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?
Questions and Answers
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?
