POO II - Classes Abstratas, Herança e Visibilidade

Introduction

This tutorial will guide you through the concepts of abstract classes, inheritance, and visibility in object-oriented programming using the principles discussed in the video "POO II - Classes Abstratas, Herança e Visibilidade". Understanding these concepts is crucial for creating robust and reusable code in languages like Java, C#, or Python.

Step 1: Defining an Abstract Class

An abstract class serves as a template for other classes. It cannot be instantiated on its own. Here’s how to define one:

• Use the keyword abstract in the class declaration.
• Include at least one abstract method (a method without implementation) in the class.

Example

public abstract class Animal {
    abstract void makeSound();
}

Tip: Abstract classes can also include concrete methods (methods with implementation) to provide shared functionality for derived classes.

Step 2: Creating Subclasses

Once you have an abstract class, you can create subclasses that inherit from it. Each subclass must implement the abstract methods defined in the abstract class.

Steps to Create a Subclass

1. Use the extends keyword (in Java) to inherit from the abstract class.
2. Implement the abstract methods.

Example

public class Dog extends Animal {
    @Override
    void makeSound() {
        System.out.println("Bark");
    }
}

Common Pitfall: Forgetting to implement all abstract methods in the subclass will result in a compilation error.

Step 3: Implementing Abstract Methods

Ensure that each subclass provides a unique implementation of the abstract methods. This allows for polymorphism, where different subclasses can be treated as instances of the abstract class.

Example

public class Cat extends Animal {
    @Override
    void makeSound() {
        System.out.println("Meow");
    }
}

Practical Advice: Use interfaces if you require a contract for methods without shared code among classes.

Step 4: Understanding Visibility

Visibility controls how classes and their members can be accessed. Use the following keywords to specify visibility:

• public: Accessible from anywhere.
• protected: Accessible within the same package and subclasses.
• private: Accessible only within the class.

Example

public class Animal {
    private String name; // Only accessible within Animal class
    protected int age;   // Accessible in subclasses and same package
}

Tip: Use protected for members that should be accessible in subclasses, while keeping them hidden from other classes.

Conclusion

In this tutorial, you learned how to define abstract classes, create subclasses, implement abstract methods, and understand visibility in object-oriented programming. By leveraging these concepts, you can create flexible and maintainable code.

Next steps could include exploring interfaces for multiple inheritance and practicing by creating a small project using these concepts. Happy coding!