Computer Science
Java Classes And Objects
In Java, classes are used to define the blueprint for creating objects. Objects are instances of classes and represent real-world entities. Classes encapsulate data and behavior, while objects interact with each other through methods and attributes. This object-oriented approach allows for modular and reusable code, making Java a popular choice for building complex software systems.
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No longer available |Learn moreThe Java Workshop
A Practical, No-Nonsense Introduction to Java Development
- David Cuartielles, Andreas Göransson, Eric Foster-Johnson(Authors)
- 2019(Publication Date)
- Packt Publishing(Publisher)
3. Object-Oriented Programming
OverviewIn this chapter, we will consider the way in which Java implements object-oriented programming (OOP ) concepts. For these purposes, you will first practice creating and instantiating your own classes so that you can later create methods that can handle data within them. We will then take you through how to code recursive methods, and even how to override existing methods in favor of your own. By the end of the chapter, you will be fully equipped to overload the definition of methods in order to accommodate different scenarios with different parameters to the same method or constructor, and annotate code to inform the compiler about specific actions that must be taken.Introduction
A Java class is a template that is used to define data types. Classes are composed of objects carrying data and methods that are used to perform operations on that data. Classes can be self-contained, extend other classes with new functionalities, or implement features from other classes. In a way, classes are categories that allow us to define what kind of data can be stored within them, as well as the ways in which that data can be handled.Classes tell the compiler how to build a certain object during runtime. Refer to the explanation of what objects are in the Working with Objects in Java topic.The basic structure of a class definition looks like this: class <name> { fields; methods; } NoteClass names should start with a capital letter, as in TheClass , Animal , WordCount , or any other string that somehow expresses the main purpose of the class. If contained in a separate file, the filename containing the source should be named like the class: TheClass.java , Animal.java , and so on.The Anatomy of a Class
There are different software components in classes. The following example shows a class that includes some of the main ones.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 3 Class and Instance (Computer Science) Class (computer science) In object-oriented programming, a class is a construct that is used as a blueprint (or template) to create objects of that class. This blueprint describes the state and behavior that the objects of the class all share. An object of a given class is called an instance of the class. The class that contains (and was used to create) that instance can be considered as the type of that object, e.g. an object instance of the Fruit class would be of the type Fruit. A class usually represents a noun, such as a person, place or (possibly quite abstract) thing - it is a model of a concept within a computer program. Fundamentally, it encapsulates the state and behavior of the concept it represents. It encapsulates state through data placeholders called attributes (or member variables or instance variables ); it encapsulates behavior through reusable sections of code called methods . More technically, a class is a cohesive package that consists of a particular kind of metadata. A class has both an interface and a structure. The interface describes how to interact with the class and its instances using methods, while the structure describes how the data is partitioned into attributes within an instance. A class may also have a representation (metaobject) at run time, which provides run time support for manipulating the class-related metadata. In object-oriented design, a class is the most specific type of an object in relation to a specific layer. Programming languages that support classes subtly differ in their support for various class-related features. Most support various forms of class inheritance. Many languages also support features providing encapsulation, such as access specifiers. Reasons for using classes Computer programs usually model aspects of some real or abstract world (the Domain).
eBook - ePubBeginning Java Programming
The Object-Oriented Approach
- Bart Baesens, Aimee Backiel, Seppe vanden Broucke(Authors)
- 2015(Publication Date)
- Wrox(Publisher)
inheritance, which is a concept to allow for extending objects and enabling code reuse. You will revisit these concepts in more detail in Chapter 8, when you delve deeper into object-oriented concepts. For now, you’ll see how the object-oriented concepts you have seen so far—the classes, objects, variables (data), and methods (behavior)—are used in Java.CLASSES AND OBJECTS IN JAVA
Now that you have gained knowledge on the basics of Java, it is time to move on to the topics that make Java an object-oriented language: classes and objects. The following sections will guide you through the concept of a class, which serves as a declaration, or blueprint, for objects, which can be instantiated from classes.Defining Classes in Java
As discussed in Chapter 2, Java is a “pure” object-oriented programming language, meaning that there are no standalone constants, variables, or functions. It is not possible to define such standalone elements, and everything is thus accessed through classes and objects. Before version 5 of Java, primitive types (such as int and double ) were not represented as objects, a decision made by Java’s designers for performance reasons. Due to this, Java was not considered to be a pure object-oriented programming language. However, Java 5 introduced a concept called autoboxing, where programmers can access primitive types as if they were instances of their wrapper class.AUTOBOXING
Autoboxing is an automatic conversion made by the Java compiler between primitive types and their corresponding wrapper classes. For example, converting a double to a Double is called boxing, and converting a Double back to a double
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 3 Class and Instance (Computer Science) Class (computer science) In object-oriented programming, a class is a construct that is used as a blueprint (or template) to create objects of that class. This blueprint describes the state and behavior that the objects of the class all share. An object of a given class is called an instance of the class. The class that contains (and was used to create) that instance can be considered as the type of that object, e.g. an object instance of the Fruit class would be of the type Fruit. A class usually represents a noun, such as a person, place or (possibly quite abstract) thing - it is a model of a concept within a computer program. Fundamentally, it enca-psulates the state and behavior of the concept it represents. It encapsulates state through data placeholders called attributes (or member variables or instance variables ); it encapsulates behavior through reusable sections of code called methods . More technically, a class is a cohesive package that consists of a particular kind of metadata. A class has both an interface and a structure. The interface describes how to interact with the class and its instances using methods, while the structure describes how the data is partitioned into attributes within an instance. A class may also have a representation (metaobject) at run time, which provides run time support for manipulating the class-related metadata. In object-oriented design, a class is the most specific type of an object in relation to a specific layer. Programming languages that support classes subtly differ in their support for various class-related features. Most support various forms of class inheritance. Many languages also support features providing encapsulation, such as access specifiers. Reasons for using classes Computer programs usually model aspects of some real or abstract world (the Domain).
- Jocelyn O. Padallan(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
A class can consists of any of the following types of variable. • Local variables: The local variables are the variables that are defined inside methods, constructors or blocks. The local variables are usually declared and initialized within the method and the variable will be destroyed when the method has completely executed. • Instance variables: The kind of variables that exist within a class but are present outside any method are known as the Instance variables. This type of variables is initialized when the class is instantiated. Instance variables can be accessed from inside any method, constructor or blocks of that particular class. • Class variables: The variables that are declared within a class, outside any method, along with the static keyword are known as Class variables. 3.5.2. Objects in Java Programming It is the fundamental unit of the Object-oriented Programming. The real-life Introduction to Computer Programming and Numerical Methods 82 entities are denoted by the objects. A typical Java program creates many objects which interact with the help of invoking methods. An object contains: State: Attributes of an object represent the state. The state depicts the properties of an object. Behavior: The behavior explains the methods of an object. Also, it depicts the response of an object with other objects. Identity: Identity makes the object unique while enabling one object to interact with the other objects. Example of an object: dog Table 3.1. Difference between Class and Objects in Java Object Class Object is defined as an instance of a class. Class is defined as a blueprint or tem -plate from which objects are created. Object is considered as a real-world entity like laptop, bed, mouse, chair, pen, mobile, keyboard, etc. Class is defined as a group of similar objects. Object is a physical entity.
No longer available |Learn moreLearn Java 12 Programming
A step-by-step guide to learning essential concepts in Java SE 10, 11, and 12
- Nick Samoylov(Author)
- 2019(Publication Date)
- Packt Publishing(Publisher)
Java Object-Oriented Programming (OOP)
Object-Oriented Programming (OOP ) was born out of the necessity for better control over concurrent modification of the shared data, which was the curse of pre-OOP programming. The core of the idea was not to allow direct access to the data but to do it only through the dedicated layer of code. Since the data needs to be passed around and modified in the process, the concept of an object was conceived. In the most general sense, an object is a set of data that can be passed around and accessed only through the set of methods passed along too. This data is said to compose an object state , while the methods constitute the object behavior . The object state is hidden (encapsulated ) from direct access.Each object is constructed based on a certain template called a class . In other words, a class defines a class of objects. Each object has a certain interface , a formal definition of the way other objects can interact with it. Originally, it was said that one object sends a message to another object by calling its method. But this terminology did not hold, especially after actual message-based protocols and systems were introduced.To avoid code duplication, a parent-child relationship between objects was introduced: it was said that one class can inherit behavior from another class. In such a relationship, the first class is called a child class , or a subclass , while the second is called a parent or base class or superclass .Another form of relationship was defined between classes and interfaces: it is said that a class can implement an interface. Since an interface describes how you can interact with an object, but not how an object responds to the interaction, different objects can behave differently while implementing the same interface.In Java, a class can have only one direct parent but can implement many interfaces. The ability to behave as any of its ancestors and adhere to multiple interfaces is called polymorphism
eBook - ePub- Nick Samoylov(Author)
- 2022(Publication Date)
- Packt Publishing(Publisher)
Chapter 2 : Java Object-Oriented Programming (OOP)Object-Oriented Programming (OOP ) was born out of the necessity for better control over the concurrent modification of shared data, which was the curse of pre-OOP programming. The core of the idea was not to allow direct access to data and instead, do it only through a dedicated layer of code. Since data needs to be passed around and modified in the process, the concept of an object was conceived. In the most general sense, an object is a set of data that can be passed around and accessed only through the set of methods passed along too. This data is said to compose an object state , while the methods constitute the object behavior . The object state is hidden (encapsulated ) from direct access.Each object is constructed based on a certain template called a class . In other words, a class defines a class of objects. Each object has a certain interface , a formal definition of the way other objects can interact with it. Originally, one object would send a message to another object by calling its method. But this terminology did not hold, especially after actual message-based protocols and systems were introduced.To avoid code duplication, a parent-child relationship between objects was introduced – one class can inherit behavior from another class. In such a relationship, the first class is called a child class , or subclass , while the second is called a parent , base class , or superclass .Another form of relationship was defined between classes and interfaces – a class can implement
eBook - PDFJava Concepts
Late Objects
- Cay S. Horstmann(Author)
- 2016(Publication Date)
- Wiley(Publisher)
In an object-oriented program, you don’t simply manipulate numbers and strings, but you work with objects that are meaningful for your application. Objects with the same behavior (such as the windmills shown here) are grouped into classes. A programmer provides the desired behavior by specifying and implementing methods for these classes. In this chapter, you will learn how to discover, specify, and implement your own classes, and how to use them in your programs. 8.1 Object-Oriented Programming You have learned how to structure your programs by decomposing tasks into meth- ods. This is an excellent practice, but experience shows that it does not go far enough. It is difficult to understand and update a program that consists of a large collection of methods. To overcome this problem, computer scientists invented object-oriented programming, a programming style in which tasks are solved by collaborating objects. Each object has its own set of data, together with a set of methods that act upon the data. You have already experienced this programming style when you used strings, the System.out object, or a Scanner object. Each of these objects has a set of methods. For example, you can use the length and substring methods to work with String objects. When you develop an object-oriented program, you create your own objects that describe what is important in your application. For example, in a student database you might work with Student and Course objects. Of course, then you must supply methods for these objects. In Java, a programmer doesn’t implement a single object. Instead, the program- mer provides a class. A class describes a set of objects with the same behavior. For example, the String class describes the behavior of all strings. The class specifies how A Car class describes passenger vehicles that can carry 4–5 people and a small amount of luggage. A class describes a set of objects with the same behavior. © Cameron Strathdee/iStockphoto. Media Bakery.
eBook - PDF- Doug Lowe(Author)
- 2023(Publication Date)
- For Dummies(Publisher)
3 Object-Oriented Programming Contents at a Glance CHAPTER 1: Understanding Object-Oriented Programming 239 CHAPTER 2: Making Your Own Classes 253 CHAPTER 3: Working with Statics 273 CHAPTER 4: Using Subclasses and Inheritance 283 CHAPTER 5: Using Abstract Classes and Interfaces 305 CHAPTER 6: Using the Object and Class Classes 327 CHAPTER 7: Using Inner Classes and Anonymous Classes 355 CHAPTER 8: Working with Packages and the Java Module System 365 CHAPTER 1 Understanding Object-Oriented Programming 239 Understanding Object- Oriented Programming T his chapter is a basic introduction to object-oriented programming. It introduces some of the basic concepts and terms you need to know as you get a handle on the specific details of how object-oriented programming works in Java. If you’re more of a hands-on type, you may want to skip this chapter and go straight to Book 3, Chapter 2, where you find out how to create your own classes in Java. You can always return to this chapter later to review the basic concepts that drive object-oriented programming. Either way is okay by me. I get paid the same whether you read this chapter now or skip it and come back to it later. Chapter 1 IN THIS CHAPTER » Looking at what object-oriented programming is » Understanding objects and classes » Investigating inheritance and interfaces » Designing programs with objects » Diagramming with UML 240 BOOK 3 Object-Oriented Programming What Is Object-Oriented Programming? The term object-oriented programming means many different things. But at its heart, object-oriented programming is a type of computer programming based on the premise that all programs are essentially computer-based simulations of real-world objects or abstract concepts. For example: » Flight-simulator programs attempt to mimic the behavior of real airplanes. Some do an amazingly good job; military and commercial pilots train on them.
eBook - PDF- Kyla McMullen, Elizabeth Matthews, June Jamrich Parsons, , Kyla McMullen, Kyla McMullen, Elizabeth Matthews, June Jamrich Parsons(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
An instance of a class is an ____________________. A methods; member variables; object Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. PROGRAMMING WITH C++ 238 Objects as Variables (13.2.4, 13.2.5) When you begin programming, you use simple variables, referred to as primitive data types or built-in data types, that hold a single value such as an integer, decimal, character, or Boolean value. In object-oriented pro- gramming, objects are treated as variables. They are considered complex data types because they can store more than one type of primitive data types. For example, my_celica has attributes that are of string, integer, and Boolean data types. In code, both primitive data types and objects are referred to by their variable names. For example, the vari- able name my_celica refers to a specific car, the one you created from the Car class. You can use the public mutators in the Car class to set the member variables of the Car objects. Create as many instances of the Car variable as you need. Figure 13-5 shows code that creates three new Car objects named my_corolla, my_beetle, and my_lamborghini. Figure 13-5 Declaring three Car objects int main() { Car my_corolla; Car my_beetle; Car my_lamborghini; return 0; } Object-Oriented Features and Principles (13.2.6, 13.2.7) One of the goals of object-oriented programming is to make code easier to use. Bundling data with the actions they can perform makes objects easier to use, and this is called encapsulation. A class encapsulates, or encloses, its attributes and methods into an object.
- Mark C. Lewis, Lisa L. Lacher(Authors)
- 2017(Publication Date)
- Chapman and Hall/CRC(Publisher)
You have one cookie cutter, but you can use it to create many different cookies. Every cookie made with a particular cookie cutter will be the same in certain key ways. In the same way, a blueprint can be used to make many different houses, but they will all come out as close copies of one another. The class es that you write in your code serve as the blueprints for making instance objects. The declarations in a class tell us what members go into the instance objects created 1 Both Java and Python are also class based. Most object-orientated programming languages are. The most notable exception is JavaScript, which allows you to create objects and add things to them without having classes. JavaScript 6, more formally known as ECMAScript 6, adds class syntax to the language, but it is only syntactic sugar on top of the prototype-based object-orientation that the language has provided since its creation. Basics of Object-Orientation and Software Development 53 from that class. The members can be any type of declaration in Scala. We will typically focus on member data, declared with val or var , and member functions, declared with def . 2 The member data is sometimes referred to as properties and the member functions are almost always referred to as methods. The syntax for a class is as follows. class TypeName(arguments) { // Methods and Member Data } The curly braces on a class declaration, like all curly braces in Scala, define a new scope. This scope is associated with the class and anything you want to put in the class goes inside of them. You can also put normal code inside of the curly braces. That code will be executed every time an object is instantiated with new . Like code in a function, code put in the class is executed from top to bottom. It is important to note that while you can use things that are declared in the body of class es before their declaration, you need to be careful of this when it comes to code and member data.
eBook - PDF- John Paul Mueller(Author)
- 2020(Publication Date)
- For Dummies(Publisher)
What are you standing in inside? Okay, you get the idea. Everything you can imagine is a thing — or, to use another term, an object . Over the years, researchers in the world of computer programming have figured out that one of the better ways to program computers is to divide whatever it is you’re trying to model into a bunch of objects. These objects have methods (capa-bilities) and properties (characteristics). (Eventually they have relationships, but that comes later.) In this chapter, you see how to make use of objects to create a software applica-tion. In the process, you get to twist some of the nuts and bolts of C ++ that relate to objects and get tips on how to get the most out of them. You don’t have to type the source code for this chapter manually. In fact, using the downloadable source is a lot easier. You can find the source for this chapter in the CPP_AIO4BookIIChapter03 folder of the downloadable source. See the Introduction for details on how to find these source files. Chapter 3 IN THIS CHAPTER » Recognizing objects so that you can create classes » Encapsulating classes into self-contained capsules » Building hierarchies of classes through inheritance 310 BOOK 2 Understanding Objects and Classes Recognizing Objects Think of an object as anything that a computer can describe. Just as physical things have characteristics, such as size, weight, and color, objects in an application can have properties — say, a particular number of accounts, an engine, or even other objects that it contains., A car, for example, contains engines, doors, and other objects. Further, just as you can use real-world objects in certain ways because they have particular capabilities, an object in an application can use methods. For example, it might be able to withdraw money or send a message or connect to the Internet. Here’s an example of modeling an object by thinking about how it’s put together and how you use it. Outside, in front of your house, you might see a mailbox.
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