Index

1. 1. Inheritance in Object-Oriented Design
2. 2. Design Patterns Introduction and Classification
3. 3. Iterator Pattern

1. Inheritance in Object-Oriented Design:

Inheritance allows one class (called the subclass or derived class) to inherit the fields and methods of another class (called the superclass or base class). This promotes code reuse and establishes a natural hierarchy between classes.

• Superclass: The parent class from which properties and methods are inherited.
• Subclass: The child class that inherits from the superclass.

Key Concepts:

• A subclass inherits all non-private members (fields and methods) of its superclass.
• Subclasses can override methods of the superclass to provide a more specific implementation.
• In Java, inheritance is implemented using the extends keyword.

Example:

class Animal {
    protected String name;

    public void eat() {
        System.out.println("This animal eats food.");
    }
}

class Dog extends Animal {  // Inherits from Animal
    public Dog(String name) {
        this.name = name;  // Inherited from Animal
    }

    @Override
    public void eat() {
        System.out.println(name + " eats dog food.");  // Overridden method
    }
}

In this example:

• The Dog class inherits the name field and eat() method from the Animal class.
• The Dog class overrides the eat() method to give a more specific behavior.

Benefits of Inheritance:

• Code Reusability: You don't need to rewrite common methods for each subclass.
• Extensibility: Subclasses can extend the functionality of a superclass while still reusing its code.
• Method Overriding: Allows you to provide a subclass-specific implementation of a method while maintaining a common interface.

2. Design Patterns: Introduction and Classification

Design patterns are typical solutions to common problems in software design. They represent best practices and provide general templates that can be applied to solve recurring design challenges.

Introduction to Design Patterns:

• Creational Patterns: Deal with object creation mechanisms, trying to create objects in a manner suitable for the situation. Examples include Singleton and Factory patterns.
• Structural Patterns: Focus on how objects and classes are composed to form larger structures. Examples include Adapter, Decorator, and Composite patterns.
• Behavioral Patterns: Deal with object collaboration and interaction. Examples include Observer, Strategy, and Iterator patterns.

Classification of Design Patterns:

1. Creational Patterns:

   • Focus on how objects are created.
   • Example: Factory Pattern, Singleton Pattern.

2. Structural Patterns:

   • Deal with object composition, forming larger structures.
   • Example: Adapter Pattern, Composite Pattern.

3. Behavioral Patterns:

   • Focus on how objects interact with one another.
   • Example: Observer Pattern, Iterator Pattern.

3. Iterator Pattern:

The Iterator pattern is a behavioral design pattern that provides a way to access elements of a collection (like a list or array) sequentially without exposing the underlying representation.

Why Use the Iterator Pattern?

• It decouples the client from the underlying structure of the collection.
• The client can focus on traversing the collection without worrying about how the collection is internally implemented.

Example:

import java.util.Iterator;
import java.util.ArrayList;

class Main {
    public static void main(String[] args) {
        ArrayList<String> animals = new ArrayList<>();
        animals.add("Cat");
        animals.add("Dog");
        animals.add("Cow");

        // Using an iterator to traverse the collection
        Iterator<String> iterator = animals.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

In this example:

• An ArrayList of animals is created.
• The Iterator is used to traverse the list without exposing the internal structure of ArrayList.

Benefits of the Iterator Pattern:

• Provides a standard way to loop through different types of collections.
• Makes code cleaner and easier to maintain.