Week 2 -Object-Oriented Programming & GitHub

Welcome to Java!

• Introduction to Java focused on Object-Oriented Programming (OOP).

• Week Two of the course.

Week Two Objectives

• L02-01: Using Java Methods

• L02-02: Using Java Recursive Methods

• L02-03: Learning Object-Oriented Programming Principles

• L02-04: Java Object & Class

• L02-05: GitHub Setting Up

Using Java Methods

Overview

• A method is a block of code that runs when called.

• Methods can take parameters and return results.

• Essential for code reuse.

Example Code

• Example Java code for method creation (incomplete code).

What is a Method?

• A method performs certain functions and actions.

• Methods allow passing parameters and returning results.

• Reusability: code can be defined once and utilized multiple times.

Declaring a Java Method

Syntax

• returnType methodName(datatype parameter1, datatype parameter2, ...) { }

• Components:

  • returnType: Defines what value is returned (or 'void' if none).

  • methodName: Identifier for the method.

  • method body: Enclosed in {} containing the statements.

Example Code

• Example of a method that adds two numbers:

int addNumbers(int numberOne, int numberTwo) {
    int result = numberOne + numberTwo;
    return result;
}

Using a Method

Example Call

• int answer = addNumbers(20, 30);

Complete Syntax for Declaring a Method

• modifier static returnType nameOfMethod(parameter1 datatype parameter01, ...) { }

Example Code

• Example method for adding two doubles:

public static double add(double numberOne, double numberTwo) {
    return numberOne + numberTwo;
}

• modifier: Defines access level (e.g., public, private).

• parameters: Values passed into the method.

Exercises

Exercise 02

• Create a method that passes two numbers and returns the largest.

Exercise 03

• Implement a basic calculator using Java methods:

  • Take two numbers as input

  • Take an operator input (+, -, *, /)

  • Display the result

Using Java Methods Recursively

Overview

• Recursion: when a function calls itself.

• Simplifies complex problems into manageable ones.

Recursion Example

Adding Numbers

• Sum(n) = 0 + 1 + 2 + ... + n

• For n=10, calculate Sum(10) using recursion.

Recursive Relationship

• Sum(n) = n + sum(n-1)

• Base Case: Sum(0) = 0

Example Code

public class Example {
    public static void main(String[] args) {
        int result = sum(10);
        System.out.println(result);
    }
    public static int sum(int n) {
        if (n > 0) {
            return n + sum(n - 1);
        } else {
            return 0;
        }
    }
}

Exercises on Recursion

Exercise 04

• Write a program to find the factorial of a number using recursion.

• Definition: factorial of n (n!) = 1 * 2 * ... * n.

Object-Oriented Programming Principles

Introduction

• OOP: modular, reusable software systems modeled as objects with attributes and behaviors.

OOP Advantages

Key Concepts

• Modularity: Creating self-contained objects to promote reusable designs.

• Code Organization: Makes code easier to understand and maintain.

• Encapsulation: Hides internal workings of an object for improved data security.

• Inheritance: Allows subclasses to inherit properties from superclasses, promoting code reuse.

• Abstraction: Focuses on high-level operations while hiding complex implementation.

• Polymorphism: Enables objects to respond to method calls in multiple ways.

Modeling in OOP

Real-World Entities

• OOP models real-world concepts, improving developer-stakeholder communication.

Collaboration & Software Design

• Supports team collaboration; encourages well-planned software architecture.

Industry Standard

• Languages like Java, C++, and Python support OOP, establishing it as a common programming approach.

Java Object & Class

Classes vs. Objects

• Class: Blueprint for creating objects, defining properties and behaviors.

• Object: Instance of a class representing specific entities with data and operations.

Class Syntax

• class {ClassName} { }

Example Code

public class Person {
    String name;
    int age;
    void walk() {
        System.out.println("walking...");
    }
}

Creating Objects in Java

Syntax

• {ClassName} {ObjectName} = new {ClassName}();

Example

• Person personOne = new Person();

Accessing Attributes

• Use dot operator:

  • E.g., personOne.name = "John";

Declaring, Instantiating, and Initializing an Object

Steps

1. Declaration: Person person;

2. Instantiation: person = new Person();

3. Initialization: Classes provide constructors for object initialization.

Exercises

Exercise 05 - Modeling a Book

• Create a Java class representing a book with attributes: title, author, isbn, publishedYear.

• Include methods barrow() and return().

Exercise 06 - Modeling a Car

• Define a class named Car with attributes for make, model, year, color, vehicle number.

• Include methods start() and stop().

Exercise 07 - Modeling a Student

• Define a class named Student with appropriate attributes and methods.

GitHub and Version Control

What is Git?

• A distributed, open-source version control system for tracking code changes, merging, and reverting.

• Industry standard for developers and data scientists.

How Git Works

• Stores files and history in a local repository; creates commits.

• Commits are snapshots linked in a history graph.

Branching

• Branches allow parallel works without interference; can be merged back to the main version.

Commits

• Files can be in modified, staged, or committed states.

Setting Up Git and GitHub

• Install Git on Windows through download link.

• Create a GitHub account and repository.

Configuring GitHub

• Configure user name and email in command line.

Clone, Initialize, and Commit

• Clone repository via HTTPS link; initialize a new repository with Git commands.

Basic Git Commands

• git init: Creates a local repo.

• git clone <url>: Copies a remote repo.

• git add <file>: Stages files for commit.

• git commit -m "Message": Creates a snapshot of changes.

• git push: Sends commits to the remote repo.

• Further commands for managing branches, viewing remotes, and merging.