OBJECT-ORIENTED PROGRAMMING CONCEPTS (Review)

What is an Object? What is an Object? Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors - wagging, barking, eating. An object is an instance of a class. If we consider a dog, then its state is - name, breed, color, and the behavior is - barking, wagging, running

What is a Class? What is a Class? A class can be defined as a template/blue print that describes the behaviors/states that object of its type. support. A class can contain any of the following variable types: Local variables: Variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed. Local variables: Variables defined inside methods, constructors or blocks are called local variables. The variable will be declared and initialized within the method and the variable will be destroyed when the method has completed. Instance variables: Instance variables are variables within a class but outside any method. These variables are instantiated when the class is loaded. Instance variables can be accessed from inside any method, constructor or blocks of that particular class. Instance variables: Instance variables are variables within a class but outside any method. These variables are instantiated when the class is loaded. Instance variables can be accessed from inside any method, constructor or blocks of that particular class. Class variables: Class variables are variables declared with in a class, outside any method, with the static keyword. Class variables: Class variables are variables declared with in a class, outside any method, with the static keyword.

What is Inheritance? What is Inheritance? Object-oriented programming allows classes to inherit commonly used state and behavior from other classes. Different kinds of objects often have a certain amount in common with each other. Mountain bikes, road bikes, and tandem bikes, for example, all share the characteristics of bicycles (current speed, current pedal cadence, current gear). Yet each also defines additional features that make them different: tandem bicycles have two seats and two sets of handlebars; road bikes have drop handlebars; some mountain bikes have an additional chain ring, giving them a lower gear ratio Bicycle now becomes the superclass of MountainBike, RoadBike, and TandemBike. In the Java programming language, each class is allowed to have one direct superclass, and each superclass has the potential for an unlimited number of subclasses

When we talk about inheritance, the most commonly used keyword would be extends and implements The syntax for creating a subclass is simple. At the beginning of your class declaration, use the extends keyword, followed by the name of the class to inherit from: class MountainBike extends Bicycle { class MountainBike extends Bicycle { // new fields and methods defining // new fields and methods defining // a mountain bike would go here // a mountain bike would go here }

The implements keyword is used by classes by inherit from interfaces. Interfaces can never be extended by the classes. public interface Animal { } public class Mammal implements Animal{ public class Mammal implements Animal{}

What Is an Interface? What Is an Interface? An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. An interface is a collection of abstract methods. A class implements an interface, thereby inheriting the abstract methods of the interface. An interface is not a class. Writing an interface is similar to writing a class, but they are two different concepts. A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements. interface Bicycle { // wheel revolutions per minute // wheel revolutions per minute void changeCadence(int newValue); void changeCadence(int newValue); void changeGear(int newValue); void changeGear(int newValue); void speedUp(int increment); void speedUp(int increment); void applyBrakes(int decrement); void applyBrakes(int decrement); }

What Is a Package? What Is a Package? A package is a namespace that organizes a set of related classes and interfaces Conceptually you can think of packages as being similar to different folders on your computer You might keep HTML pages in one folder, images in another, and scripts or applications in yet another Keep things organized by placing related classes and interfaces into packages

The Java platform provides an enormous class library (a set of packages) suitable for use in your own applications. This library is known as the "Application Programming Interface", or "API" for short. Its packages represent the tasks most commonly associated with general-purpose programming. This library is known as the "Application Programming Interface", or "API" for short. Its packages represent the tasks most commonly associated with general-purpose programming.

For example, a String object contains state and behavior for character strings; a File object allows a programmer to easily create, delete, inspect, compare, or modify a file on the filesystem; a Socket object allows for the creation and use of network sockets; various GUI objects control buttons and checkboxes and anything else related to graphical user interfaces. package insurance; public class Policy{ public class Policy{ //Code goes here }

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