Chapter 6: Object-Oriented Programming (OOP)

Introduction:

Object-Oriented Programming (OOP) is a programming paradigm that focuses on organizing code around objects, which are instances of classes. In this chapter, we will explore the core concepts of OOP in Java, including classes, objects, inheritance, and polymorphism.

Classes and Objects:

Introduction to Classes and Objects:

A class is a blueprint or template for creating objects. It defines the properties (attributes) and behaviors (methods) that objects of that class possess. Objects are instances of a class.

Example:

java

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public class Car {

    String color;

    int year;

    

    void startEngine() {

        // Code to start the car's engine

    }

}

Creating Objects and Accessing Members:

To use a class, you need to create objects from it. Objects have access to the members (variables and methods) defined within the class, which can be accessed using the dot notation.

Example:

java

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Car myCar = new Car();  // Create an object of the Car class

myCar.color = "Blue";  // Access and modify the color attribute

myCar.startEngine();   // Call the startEngine() method

Inheritance:

Inheritance and Superclasses:

Inheritance is a mechanism that allows a class to inherit the properties and behaviors of another class. The class being inherited from is called the superclass or parent class, and the class inheriting from it is called the subclass or child class.

Example:

java

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public class Animal {

    void eat() {

        System.out.println("Animal is eating.");

    }

}

public class Dog extends Animal {

    void bark() {

        System.out.println("Dog is barking.");

    }

}

Overriding and Super Keyword:

A subclass can override methods from its superclass to provide its own implementation. The super keyword is used to refer to the superclass and invoke its methods or constructors.

Example:

java

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public class Animal {

    void makeSound() {

        System.out.println("Animal is making a sound.");

    }

}

public class Dog extends Animal {

    @Override

    void makeSound() {

        System.out.println("Dog is barking.");

    }

    

    void greet() {

        super.makeSound();  // Call the makeSound() method of the superclass

    }

}

Polymorphism:

Polymorphism and Method Overloading:

Polymorphism allows objects of different classes to be treated as objects of a common superclass. Method overloading is a form of polymorphism that enables a class to have multiple methods with the same name but different parameters.

Example:

java

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public class MathUtils {

    int add(int a, int b) {

        return a + b;

    }

    

    double add(double a, double b) {

        return a + b;

    }

}

Polymorphism and Method Overriding:

Method overriding is another form of polymorphism that occurs when a subclass provides a specific implementation of a method that is already defined in its superclass.

Example:

java

_____________________________________________

public class Animal {

    void makeSound() {

        System.out.println("Animal is making a sound.");

    }

}

public class Cat extends Animal {

    @Override

    void makeSound() {

        System.out.println("Cat is meowing.");

    }

}

Conclusion:

In this chapter, we explored the core concepts of Object-Oriented Programming (OOP) in Java. We discussed classes, objects, inheritance, and polymorphism. By using OOP principles, you can create more organized, modular, and flexible programs. In the following chapters, we will delve deeper into more advanced Java concepts.

Note: Make sure to include additional chapters and topics to cover all the essential aspects of Java programming in your book. The provided content is a sample for Chapter 6 only.