The document provides an overview of key Java concepts including classes, objects, methods, constructors, inheritance, polymorphism, abstraction, and encapsulation. It defines classes like Circle and Shape that demonstrate these concepts. Circles have fields like radius and methods like area() and circumference(). The Shape class is abstract with abstract area() and circumference() methods that concrete subclasses like Circle must implement. Access modifiers like public, private, and protected are used to control access to class members.
OOPS Concepts, Java Evolution, Class Object basic, Class Object Constructor overloading, Inheritance, Array and String, Final Abstract class and interfaces, Exceptions, Streams, GUI Applications, Applet Programming, Network Programming and Java Sockets, Multi Threading
OOPS Concepts, Java Evolution, Class Object basic, Class Object Constructor overloading, Inheritance, Array and String, Final Abstract class and interfaces, Exceptions, Streams, GUI Applications, Applet Programming, Network Programming and Java Sockets, Multi Threading
Lara Technologies are providing Software Training Division, Java/J2ee, Android, Web Services, Logical Coding, Basics Of C Language, Soft Skills, Aptitude, Etc.
Method overloading, recursion, passing and returning objects from method, new...JAINAM KAPADIYA
Method and Method overloading
How to overload method in JAVA?
Method overloading Examples of the program.
New operator
Recursion
Passing and returning objects from methods.
Chapter 02: Classes Objects and Methods Java by Tushar B KuteTushar B Kute
The lecture was condcuted by Tushar B Kute at YCMOU, Nashik through VLC orgnanized by MSBTE. The contents can be found in book "Core Java Programming - A Practical Approach' by Laxmi Publications.
Core java training in Bangalore is one the best Training in Entire bangalore, Where you can learn Java in Shorter time. TIB Academy is the platform where you gain all you confidence back.
The Emergence of the “Church history” and the predicament of Orthodox Hierarc...Евгений Лютько
EHS Conferences 2016-17: The Church and Empire (Pollock Halls, University of Edinburgh, 26-28 July 2016) presentation for the paper "The Emergence of the “Church history” and the predicament of Orthodox Hierarchy in the Russian Empire of the early 1800s"
Lara Technologies are providing Software Training Division, Java/J2ee, Android, Web Services, Logical Coding, Basics Of C Language, Soft Skills, Aptitude, Etc.
Method overloading, recursion, passing and returning objects from method, new...JAINAM KAPADIYA
Method and Method overloading
How to overload method in JAVA?
Method overloading Examples of the program.
New operator
Recursion
Passing and returning objects from methods.
Chapter 02: Classes Objects and Methods Java by Tushar B KuteTushar B Kute
The lecture was condcuted by Tushar B Kute at YCMOU, Nashik through VLC orgnanized by MSBTE. The contents can be found in book "Core Java Programming - A Practical Approach' by Laxmi Publications.
Core java training in Bangalore is one the best Training in Entire bangalore, Where you can learn Java in Shorter time. TIB Academy is the platform where you gain all you confidence back.
The Emergence of the “Church history” and the predicament of Orthodox Hierarc...Евгений Лютько
EHS Conferences 2016-17: The Church and Empire (Pollock Halls, University of Edinburgh, 26-28 July 2016) presentation for the paper "The Emergence of the “Church history” and the predicament of Orthodox Hierarchy in the Russian Empire of the early 1800s"
With the presentation that I have named “Spend a bit, Listen a lot” I’ll talk about the basics of SDR very low cost devices, about the installation for newcomers to this world and late I’ll cover advanced topics as listening and interception of digital communication networks such as DMR, TETRA, GSM,…
Современный подход к подготовке врача-уролога: от «образования на всю жизнь» ...Игорь Шадеркин
Министерство здравоохранения и социального развития РФ
ФГУ «НИИ Урологии Росмедтехнологий»
Современный подход к подготовке врача-уролога: от «образования на всю жизнь» к «образованию через всю жизнь»
Аполихин О.И., Абдуллин И.И., Казаченко А.В.
МОСКВА 2010
Myassignmenthelpers.com is an Online service provider for Java assignments & homework problems. Our online experts provide Java Assignment help & Java homework help with aims to help college students across the globe. Our writers provide you unique data along with a plagiarised report so that you can ensure that your data is unique. Our writers are available 24*7. Please send your complete requirements at support@myassignmenthelpers.com or else attach on the website. You can also discuss the requirements with our chat agent.
UNIT - 2
ARRAY AND ITS TYPES
INHERITANCE AND ITS TYPES
THE SUPER KEYWORD
POLYMORPHISM
ABSTRACT CLASSES
INTERFACES
DECLARING INTERFACES
IMPLEMENTING INTERFACES
EXTENDED INTERFACES
EXTENDING MULTIPLE INTERFACES
PACKAGES
THE IMPORT KEYWORD
THE DIRECTORY STRUCTURE OF PACKAGES
ACCESS SPECIFIER
Object Oriented Concepts required to know about the Android Application Programming are discussed over here. Get the most of the details about each and every concept of OO paradigm so you can use them very well in Android Application Programming.
Mule Munit
1. Solution for JUnit Functional test cases By: Kiet Bui 22-Sep-2015
2. Abstract • The main motto of this white paper is what the issues to write test cases using JUnit are and how to overcome those issues.
3. Table of Contents • ABSTRACT 1. INTRODUCTION 2. PROBLEM STATEMENT 3. SOLUTION 4. BENEFITS 5. CONCLUSION 6. REFERENCES 7. ABOUT THE AUTHOR 8. ABOUT WHISHWORKS
4. Introduction • We have multiple unit test frameworks to write unit and functional test cases for our services. When we write functional test cases using JUnit we can’t mock mule components. To resolve this issues we have to use MUnit and I am going to explain what is the problem with JUnit and how to resolve using MUnit in the below.
5. Problem Statement • When we write functional test cases using JUnit, the test case will directly connect to original components like SAP, Salesforce etc. and insert/select the data. It is the issue in JUnit functional test case why because we are writing functional test cases to check whether entire functionality is working as expected or not without modifying the original components(SAP,Salesforce,Database) data, but in JUnit functional test cases it is directly connecting to original components and modifying the original data. • Examples: 1. SAP Connector • Mule flow:
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Slack (or Teams) Automation for Bonterra Impact Management (fka Social Soluti...Jeffrey Haguewood
Sidekick Solutions uses Bonterra Impact Management (fka Social Solutions Apricot) and automation solutions to integrate data for business workflows.
We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on the notifications, alerts, and approval requests using Slack for Bonterra Impact Management. The solutions covered in this webinar can also be deployed for Microsoft Teams.
Interested in deploying notification automations for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
2. UMBC CMSC 331 Java
Comments are almost like C++
The javadoc program generates HTML API documentation
from the “javadoc” style comments in your code.
/* This kind of comment can span multiple lines */
// This kind is to the end of the line
/**
* This kind of comment is a special
* ‘javadoc’ style comment
*/
3. UMBC CMSC 331 Java
An example of a class
class Person {
String name;
int age;
void birthday ( ) {
age++;
System.out.println (name +
' is now ' + age);
}
}
Variable
Method
4. UMBC CMSC 331 Java
Scoping
• As in C/C++, scope is determined by the placement of curly braces {}.
• A variable defined within a scope is available only to the end of that
scope.
{ int x = 12;
/* only x available */
{ int q = 96;
/* both x and q available */
}
/* only x available */
/* q “out of scope” */
}
{ int x = 12;
{ int x = 96; /* illegal */
}
}
This is ok in C/C++ but not in Java.
5. UMBC CMSC 331 Java
An array is an object
• Person mary = new Person ( );
• int myArray[ ] = new int[5];
• int myArray[ ] = {1, 4, 9, 16, 25};
• String languages [ ] = {"Prolog",
"Java"};
• Since arrays are objects they are allocated dynamically
• Arrays, like all objects, are subject to garbage collection
when no more references remain
– so fewer memory leaks
– Java doesn’t have pointers!
6. UMBC CMSC 331 Java
Scope of Objects
• Java objects don’t have the same lifetimes as
primitives.
• When you create a Java object using new, it hangs
around past the end of the scope.
• Here, the scope of name s is delimited by the {}s
but the String object hangs around until GC’d
{
String s = new String("a string");
} /* end of scope */
7. UMBC CMSC 331 Java
Methods, arguments and return values
• Java methods are like C/C++ functions. General case:
returnType methodName ( arg1, arg2, … argN) {
methodBody
}
The return keyword exits a method optionally with a value
int storage(String s) {return s.length() * 2;}
boolean flag() { return true; }
float naturalLogBase() { return 2.718f; }
void nothing() { return; }
void nothing2() {}
8. UMBC CMSC 331 Java
The static keyword
• Java methods and variables can be declared static
• These exist independent of any object
• This means that a Class’s
– static methods can be called even if no objects of that
class have been created and
– static data is “shared” by all instances (i.e., one rvalue
per class instead of one per instance
class StaticTest {static int i = 47;}
StaticTest st1 = new StaticTest();
StaticTest st2 = new StaticTest();
// st1.i == st2.I == 47
StaticTest.i++; // or st1.I++ or st2.I++
// st1.i == st2.I == 48
9. UMBC CMSC 331 Java
Array Operations
• Subscripts always start at 0 as in C
• Subscript checking is done automatically
• Certain operations are defined on arrays of objects,
as for other classes
– e.g. myArray.length == 5
11. Echo.java
C:UMBC331java>type echo.java
// This is the Echo example from the Sun tutorial
class echo {
public static void main(String args[]) {
for (int i=0; i < args.length; i++) {
System.out.println( args[i] );
}
}
}
C:UMBC331java>javac echo.java
C:UMBC331java>java echo this is pretty silly
this
is
pretty
silly
C:UMBC331java>
12. UMBC CMSC 331 Java
Factorial Example
/**
* This program computes the factorial of a number
*/
public class Factorial { // Define a class
public static void main(String[] args) { // The program starts here
int input = Integer.parseInt(args[0]); // Get the user's input
double result = factorial(input); // Compute the factorial
System.out.println(result); // Print out the result
} // The main() method ends here
public static double factorial(int x) { // This method computes x!
if (x < 0) // Check for bad input
return 0.0; // if bad, return 0
double fact = 1.0; // Begin with an initial value
while(x > 1) { // Loop until x equals 1
fact = fact * x; // multiply by x each time
x = x - 1; // and then decrement x
} // Jump back to the star of loop
return fact; // Return the result
} // factorial() ends here
} // The class ends here
From Java in a Nutshell
13. UMBC CMSC 331 Java
JAVA Classes
• The class is the fundamental concept in JAVA (and other
OOPLs)
• A class describes some data object(s), and the operations
(or methods) that can be applied to those objects
• Every object and method in Java belongs to a class
• Classes have data (fields) and code (methods) and classes
(member classes or inner classes)
• Static methods and fields belong to the class itself
• Others belong to instances
14. UMBC CMSC 331 Java
Example
public class Circle {
// A class field
public static final double PI= 3.14159; // A useful constant
// A class method: just compute a value based on the arguments
public static double radiansToDegrees(double rads) {
return rads * 180 / PI;
}
// An instance field
public double r; // The radius of the circle
// Two methods which operate on the instance fields of an object
public double area() { // Compute the area of the
circle
return PI * r * r;
}
public double circumference() { // Compute the circumference of
the circle
return 2 * PI * r;
}
}
15. UMBC CMSC 331 Java
Constructors
• Classes should define one or more methods to create or
construct instances of the class
• Their name is the same as the class name
– note deviation from convention that methods begin with lower case
• Constructors are differentiated by the number and types of
their arguments
– An example of overloading
• If you don’t define a constructor, a default one will be
created.
• Constructors automatically invoke the zero argument
constructor of their superclass when they begin (note that
this yields a recursive process!)
16. UMBC CMSC 331 Java
Constructor example
public class Circle {
public static final double PI = 3.14159; // A constant
public double r; // instance field holds circle’s radius
// The constructor method: initialize the radius field
public Circle(double r) { this.r = r; }
// Constructor to use if no arguments
public Circle() { r = 1.0; }
// better: public Circle() { this(1.0); }
// The instance methods: compute values based on radius
public double circumference() { return 2 * PI * r; }
public double area() { return PI * r*r; }
}
this.r refers to the r
field of the class
This() refers to a
constructor for the class
17. UMBC CMSC 331 Java
Extending a class
• Class hierarchies reflect subclass-superclass relations among
classes.
• One arranges classes in hierarchies:
– A class inherits instance variables and instance methods from all of its
superclasses. Tree -> BinaryTree -> BST
– You can specify only ONE superclass for any class.
• When a subclass-superclass chain contains multiple instance
methods with the same signature (name, arity, and argument
types), the one closest to the target instance in the subclass-
superclass chain is the one executed.
– All others are shadowed/overridden.
• Something like multiple inheritance can be done via interfaces
(more on this later)
• What’s the superclass of a class defined without an extends
clause?
18. UMBC CMSC 331 Java
Extending a class
public class PlaneCircle extends Circle {
// We automatically inherit the fields and methods of Circle,
// so we only have to put the new stuff here.
// New instance fields that store the center point of the circle
public double cx, cy;
// A new constructor method to initialize the new fields
// It uses a special syntax to invoke the Circle() constructor
public PlaneCircle(double r, double x, double y) {
super(r); // Invoke the constructor of the superclass, Circle()
this.cx = x; // Initialize the instance field cx
this.cy = y; // Initialize the instance field cy
}
// The area() and circumference() methods are inherited from Circle
// A new instance method that checks whether a point is inside the circle
// Note that it uses the inherited instance field r
public boolean isInside(double x, double y) {
double dx = x - cx, dy = y - cy; // Distance from center
double distance = Math.sqrt(dx*dx + dy*dy); // Pythagorean theorem
return (distance < r); // Returns true or false
}
}
19. UMBC CMSC 331 Java
Overloading, overwriting, and shadowing
• Overloading occurs when Java can distinguish two procedures with the
same name by examining the number or types of their parameters.
• Shadowing or overriding occurs when two procedures with the same
signature (name, the same number of parameters, and the same
parameter types) are defined in different classes, one of which is a
superclass of the other.
20. UMBC CMSC 331 Java
On designing class hierarchies
• Programs should obey the explicit-representation principle, with classes
included to reflect natural categories.
• Programs should obey the no-duplication principle, with instance methods
situated among class definitions to facilitate sharing.
• Programs should obey the look-it-up principle, with class definitions
including instance variables for stable, frequently requested information.
• Programs should obey the need-to-know principle, with public interfaces
designed to restrict instance-variable and instance-method access, thus
facilitating the improvement and maintenance of nonpublic program
elements.
• If you find yourself using the phrase an X is a Y when describing the
relation between two classes, then the X class is a subclass of the Y class.
• If you find yourself using X has a Y when describing the relation between
two classes, then instances of the Y class appear as parts of instances of the
X class.
21. UMBC CMSC 331 Java
Data hiding and encapsulation
• Data-hiding or encapsulation is an important part
of the OO paradigm.
• Classes should carefully control access to their data
and methods in order to
– Hide the irrelevant implementation-level details so they
can be easily changed
– Protect the class against accidental or malicious damage.
– Keep the externally visible class simple and easy to
document
• Java has a simple access control mechanism to help
with encapsulation
– Modifiers: public, protected, private, and package
(default)
22. UMBC CMSC 331 Java
Example
encapsulation
package shapes; // Specify a package for the class
public class Circle { // The class is still public
public static final double PI = 3.14159;
protected double r; // Radius is hidden, but visible to subclasses
// A method to enforce the restriction on the radius
// This is an implementation detail that may be of interest to subclasses
protected checkRadius(double radius) {
if (radius < 0.0)
throw new IllegalArgumentException("radius may not be negative.");
}
// The constructor method
public Circle(double r) {checkRadius(r); this.r = r; }
// Public data accessor methods
public double getRadius() { return r; };
public void setRadius(double r) { checkRadius(r); this.r = r;}
// Methods to operate on the instance field
public double area() { return PI * r * r; }
public double circumference() { return 2 * PI * r; }
}
23. UMBC CMSC 331 Java
Access control
• Access to packages
– Java offers no control mechanisms for packages.
– If you can find and read the package you can access it
• Access to classes
– All top level classes in package P are accessible
anywhere in P
– All public top-level classes in P are accessible anywhere
• Access to class members (in class C in package P)
– Public: accessible anywhere C is accessible
– Protected: accessible in P and to any of C’s subclasses
– Private: only accessible within class C
– Package: only accessible in P (the default)
25. UMBC CMSC 331 Java
Getters and setters
• A getter is a method that extracts information from an instance.
– One benefit: you can include additional computation in a getter.
• A setter is a method that inserts information into an instance (also
known as mutators).
– A setter method can check the validity of the new value (e.g., between 1
and 7) or trigger a side effect (e.g., update a display)
• Getters and setters can be used even without underlying matching
variables
• Considered good OO practice
• Essential to javabeans
• Convention: for variable fooBar of type fbtype, define
– getFooBar()
– setFooBar(fbtype x)
26. UMBC CMSC 331 Java
Example
getters and setters
package shapes; // Specify a package for the class
public class Circle { // The class is still public
// This is a generally useful constant, so we keep it public
public static final double PI = 3.14159;
protected double r; // Radius is hidden, but visible to subclasses
// A method to enforce the restriction on the radius
// This is an implementation detail that may be of interest to subclasses
protected checkRadius(double radius) {
if (radius < 0.0)
throw new IllegalArgumentException("radius may not be negative.");
}
// The constructor method
public Circle(double r) { checkRadius(r); this.r = r;}
// Public data accessor methods
public double getRadius() { return r; };
public void setRadius(double r) { checkRadius(r); this.r = r;}
// Methods to operate on the instance field
public double area() { return PI * r * r; }
public double circumference() { return 2 * PI * r; }
}
27. UMBC CMSC 331 Java
Abstract classes and methods
• Abstract vs. concrete classes
• Abstract classes can not be instantiated
public abstract class shape { }
• An abstract method is a method w/o a body
public abstract double area();
• (Only) Abstract classes can have abstract methods
• In fact, any class with an abstract method is
automatically an abstract class
28. UMBC CMSC 331 Java
Example
abstract class
public abstract class Shape {
public abstract double area(); // Abstract methods: note
public abstract double circumference();// semicolon instead of body.
}
class Circle extends Shape {
public static final double PI = 3.14159265358979323846;
protected double r; // Instance data
public Circle(double r) { this.r = r; } // Constructor
public double getRadius() { return r; } // Accessor
public double area() { return PI*r*r; } // Implementations of
public double circumference() { return 2*PI*r; } // abstract methods.
}
class Rectangle extends Shape {
protected double w, h; // Instance data
public Rectangle(double w, double h) { // Constructor
this.w = w; this.h = h;
}
public double getWidth() { return w; } // Accessor method
public double getHeight() { return h; } // Another accessor
public double area() { return w*h; } // Implementations of
public double circumference() { return 2*(w + h); } // abstract methods.
}
29. UMBC CMSC 331 Java
Syntax Notes
• No global variables
– class variables and methods may be applied to any
instance of an object
– methods may have local (private?) variables
• No pointers
– but complex data objects are “referenced”
• Other parts of Java are borrowed from PL/I,
Modula, and other languages