Questions and Exercises: Object-Oriented Programming Concepts This section explains why this is useful, and introduces you to the Application Programming Interface (API) provided by the Java platform. Placing your code into packages makes large software projects easier to manage. What Is a Package?Ī package is a namespace for organizing classes and interfaces in a logical manner. This section defines a simple interface and explains the necessary changes for any class that implements it. When a class implements an interface, it promises to provide the behavior published by that interface. What Is an Interface?Īn interface is a contract between a class and the outside world. This section explains how classes inherit state and behavior from their superclasses, and explains how to derive one class from another using the simple syntax provided by the Java programming language. Inheritance provides a powerful and natural mechanism for organizing and structuring your software. It intentionally focuses on the basics, showing how even a simple class can cleanly model state and behavior. This section defines a class that models the state and behavior of a real-world object. What Is a Class?Ī class is a blueprint or prototype from which objects are created. This lesson explains how state and behavior are represented within an object, introduces the concept of data encapsulation, and explains the benefits of designing your software in this manner. Software objects are often used to model the real-world objects that you find in everyday life. What Is an Object?Īn object is a software bundle of related state and behavior. Each discussion focuses on how these concepts relate to the real world, while simultaneously providing an introduction to the syntax of the Java programming language. This lesson will introduce you to objects, classes, inheritance, interfaces, and packages. To give you an idea about classes and objects, let's create a Cat class that represents states and behaviors of real world Cat.If you've never used an object-oriented programming language before, you'll need to learn a few basic concepts before you can begin writing any code. Instance variables are also known as member variables. Source.Ĭlasses define states as instance variables and behaviors as instance methods. Figure 1: Illustrates class and object relationship through cookie-cutter and cookies. Imagine a class as a cookie-cutter and objects as cookies. What Are Classes?Ī class is a template or blueprint from which objects are created. We’ll see what a reference type is later in this article. The important thing to remember when creating an object is: the reference type should be the same type or a super type of the object type. Instantiating a class means the same thing as creating an object. Memory is allocated in RAM whenever creating a logical object.Īn object is also referred to an instance of a class. Software objects are the actual representation of real world objects. We can actually represent a real world dog in a program as a software object by defining its states and behaviors. State tells us how the object looks or what properties it has. To illustrate, a dog has states like age, color, name, and behaviors like eating, sleeping, and running. What Are Objects?Īn object is an entity that has states and behaviors.įor example, dog, cat, and vehicle. OOP focuses on each object’s states and behaviors. Each object decides what to do with a received message. Object-oriented programming is a programming paradigm where everything is represented as an object. ― Paul Graham Fundamentals of object-oriented programming It lets you accrete programs as a series of patches. Object-oriented programming offers a sustainable way to write spaghetti code.
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