Dimensions and interfaces chapter

What are we going to see in this chapter

Main skills and concepts
• Use packages
• Understand how packages affect access
• Apply the protected
access modifier • Import packages
• Know the standard Java packages
• Understand the basic aspects of the interface
• Implement an interface
• Apply interface references
• Understand interface variables
• Extend interfaces
• Create standard and static interface methods

Packages and Interfaces:
These are innovative features that help organize and encapsulate the code.

• Packages: Group related classes and help organize the code.
• Interfaces: Define methods that a class must implement, specifying what will be done, but not how.

Packages
Package functions:
They group related parts of a program into an organized unit.
Control access between classes, allowing encapsulation.

Namespace:
Prevents class name collisions by appending the package name to each class.
Solves the naming problem in large projects, avoiding conflicts with the names of other classes or libraries.

Access Control:
Packages allow code from related classes to be accessible within the same package, but private to external code.
Facilitates the creation of standalone and encapsulated groups of classes.

Example of Packages and Interfaces

src/
  mypackage/
    MyInterface.java
    MyClass.java
  Main.java

1. Defining the Package and Interface (mypackage/MyInterface.java):

package mypackage;

// Definindo uma interface
public interface MyInterface {
    void sayHello();  // Método abstrato
}

1. Implementing the Interface in a Class (mypackage/MyClass.java):

package mypackage;

// Implementando a interface em uma classe
public class MyClass implements MyInterface {
    @Override
    public void sayHello() {
        System.out.println("Olá, Mundo! Implementando uma Interface.");
    }
}

1. Using the Class and Interface in the Main Program (Main.java):

import mypackage.MyClass;  // Importando a classe do pacote 'mypackage'

public class Main {
    public static void main(String[] args) {
        MyClass myObject = new MyClass();  // Criando uma instância de MyClass
        myObject.sayHello();  // Chamando o método implementado
    }
}

Explanation:

• Package (mypackage): The classes and interface are organized in the mypackage package, which helps structure the code and avoid name collisions.
• Interface (MyInterface): Defines an abstract sayHello method that classes implementing the interface must provide.
• Class (MyClass): Implements the interface and provides the definition of the sayHello method.
• Main program: Uses the MyClass class, which implements the interface, to call the method.

Program output:
Hello World! Implementing an Interface.

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