OOP

Java Install (Windows) Install Java on Windows and set up environment variables properly. OpenJDK link: [OpenJDK](https://openjdk.org/) Eclipse Setup Download and set up Eclipse IDE to create and run Java programs. Eclipse download: [Eclipse](https://www.eclipse.org/downloads/) VS Code Setup Install VS Code and prepare it for Java development with extensions. ...

Thinking…. Anything that can be named with a noun and has a “Value” is an object. Concepts like Fame, Beauty, or Power are objects because they contain data. States A State is the current condition of an object. Fan (Object): States are “Running” or “Static.” Human (Object): States are “Anger” (Ragg), “Happiness,” or “Sleep.” The Passport Form Analogy ...

Classes & Objects (Encapsulation) Basic introduction to encapsulation using real examples. Inheritance Basics Covers UML structure, extends, super, and type casting concepts. Static & Dynamic Polymorphism Explains compile-time and runtime polymorphism with examples. ...

File Read & Write code snippet /// Lost it :) User Input to File code snippet File Main.java, must be compile with javac ...

Dynamic CGPA Calculator Learn how to design & build a dynamic calculator that can adapt any grading system in Java. Code GradeInterval.java class GradeInterval { GradeInterval(String letter, String remark, float gradePoint, int lowMark, int highMark) { this.letter = letter; this.remark = remark; this.gradePoint = gradePoint; this.lowMark = lowMark; this.highMark = highMark; } String letter; String remark; /// excellent float gradePoint; // mark range int lowMark; int highMark; boolean contains(float mark) { return mark <= highMark && mark >= lowMark; } } GradingPointSystem.java import java.util.ArrayList; abstract class GradingPointSystem { GradingPointSystem(ArrayList<GradeInterval> grades) { this.grades = grades; } ArrayList<GradeInterval> grades; abstract double getGP(Subject subject); } Main.java import java.util.ArrayList; import java.util.Scanner; class Main { static Subject scanSubject(Scanner sc) { System.out.print("Subject name: "); String name = sc.nextLine(); System.out.print("Mark: "); float mark = sc.nextFloat(); System.out.print("Credit: "); int credit = sc.nextInt(); sc.nextLine(); return new Subject(name, mark, credit); } public static void main(String[] args) { PublicUniGradeSystem gradeSystem = new PublicUniGradeSystem(PublicUniGradeSystem.getIntervals()); float cgpa = 0; ArrayList<Subject> subjects = new ArrayList<>(); Scanner scanner = new Scanner(System.in); while (true) { System.out.print("Press y to enter subject. n to exit: "); String choice = scanner.nextLine().trim().toLowerCase(); if (choice.equals("y")) { Subject subject = scanSubject(scanner); subjects.add(subject); cgpa += gradeSystem.getGP(subject); } else if (choice.equals("n")) { break; } else { System.out.println("y for enter subject.\n n to exit"); } } scanner.close(); System.out.println("YOUr CGPA " + (cgpa / subjects.size())); } } PublicUniGradeSystem.java import java.util.ArrayList; class PublicUniGradeSystem extends GradingPointSystem { PublicUniGradeSystem(ArrayList<GradeInterval> grades) { super(grades); } static ArrayList<GradeInterval> getIntervals() { ArrayList<GradeInterval> items = new ArrayList<>(); items.add(new GradeInterval("A+", "A Plus", 4.00f, 80, 100)); items.add(new GradeInterval("A", "A Regular", 3.75f, 75, 79)); items.add(new GradeInterval("A-", "A Minus", 3.50f, 70, 74)); items.add(new GradeInterval("B+", "B Plus", 3.25f, 65, 69)); items.add(new GradeInterval("B", "B Regular", 3.00f, 60, 64)); items.add(new GradeInterval("B-", "B Minus", 2.75f, 55, 59)); items.add(new GradeInterval("C+", "C Plus", 2.50f, 50, 54)); items.add(new GradeInterval("C", "C Regular", 2.25f, 45, 49)); items.add(new GradeInterval("D", "", 2.00f, 40, 44)); items.add(new GradeInterval("F", "Fail", 0.00f, 0, 39)); return items; } @Override double getGP(Subject subject) { for (GradeInterval g : grades) { if (g.contains(subject.mark)) return g.gradePoint; } throw new IllegalArgumentException("mark is out of grade range"); } } Subject.java class Subject { Subject() { } Subject(String name, float mark, int credit) { this.name = name; this.mark = mark; this.credit = credit; } String name; float mark; int credit; double getCGPA(GradingPointSystem system) { return system.getGP(this); } } Part 2 | Reading GradingPointSystem & students marks GradeInterval.java class GradeInterval { // lowMark,highMark,letter,gradePoint,remark GradeInterval(int lowMark, int highMark, String letter, float gradePoint, String remark) { this.letter = letter; this.remark = remark; this.gradePoint = gradePoint; this.lowMark = lowMark; this.highMark = highMark; } String letter; String remark; /// excellent float gradePoint; // mark range int lowMark; int highMark; boolean contains(float mark) { return mark <= highMark && mark >= lowMark; } } GradeRepository.java import java.io.BufferedReader; import java.io.FileReader; import java.util.ArrayList; public class GradeRepository { public static final String PRIVATE_UNIVERSITIES = "assets/grade_private_universities.csv"; public static final String PUBLIC_UNIVERSITY = "assets/grade_public_university.csv"; public static final String BRAC = "assets/grade_brac.csv"; public static final String IUB = "assets/grade_iub.csv"; public static final String NSU = "assets/grade_nsu.csv"; public static final String UIU = "assets/grade_uiu.csv"; public static ArrayList<GradeInterval> loadGrades(String filePath) throws Exception { ArrayList<GradeInterval> grades = new ArrayList<>(); BufferedReader reader = new BufferedReader(new FileReader(filePath)); reader.readLine(); String line; while ((line = reader.readLine()) != null) { String[] parts = line.split(","); grades.add(new GradeInterval( Integer.parseInt(parts[0]), Integer.parseInt(parts[1]), parts[2], Float.parseFloat(parts[3]), parts[4])); } reader.close(); return grades; } } GradingPointSystem.java import java.util.ArrayList; abstract class GradingPointSystem { GradingPointSystem(ArrayList<GradeInterval> grades) { this.grades = grades; } ArrayList<GradeInterval> grades; abstract double getGP(Subject subject); } Main.java import java.util.ArrayList; import java.util.Scanner; class Main { static Subject scanSubject(Scanner sc) { System.out.print("Subject name: "); String name = sc.nextLine(); System.out.print("Mark: "); float mark = sc.nextFloat(); System.out.print("Credit: "); int credit = sc.nextInt(); sc.nextLine(); return new Subject(name, mark, credit); } static ArrayList<Subject> scanSubjects() { ArrayList<Subject> subjects = new ArrayList<>(); Scanner scanner = new Scanner(System.in); while (true) { System.out.print("Press y to enter subject. n to exit: "); String choice = scanner.nextLine().trim().toLowerCase(); if (choice.equals("y")) { Subject subject = scanSubject(scanner); subjects.add(subject); } else if (choice.equals("n")) { break; } else { System.out.println("y for enter subject.\n n to exit"); } } scanner.close(); return subjects; } public static void main(String[] args) throws Exception { PublicUniGradeSystem gradeSystem = new PublicUniGradeSystem( GradeRepository.loadGrades(GradeRepository.IUB)); ArrayList<Subject> subjects = StudentRespository.loadStudentMarks(StudentRespository.students.get("101")); float totalGradePoint = 0; int totalCredit = 0; for (Subject s : subjects) { totalGradePoint += gradeSystem.getGP(s) * s.credit; totalCredit += s.credit; } if (totalCredit > 0) System.out.println("YOUr CGPA " + (totalGradePoint / totalCredit)); else System.out.println("No subject has been added"); } } PublicUniGradeSystem.java import java.util.ArrayList; class PublicUniGradeSystem extends GradingPointSystem { PublicUniGradeSystem(ArrayList<GradeInterval> grades) { super(grades); } @Override double getGP(Subject subject) { for (GradeInterval g : grades) { if (g.contains(subject.mark)) return g.gradePoint; } throw new IllegalArgumentException("mark is out of grade range"); } } StudentRespository.java import java.io.BufferedReader; import java.io.FileReader; import java.util.ArrayList; import java.util.HashMap; public class StudentRespository { public static HashMap<String, String> students = new HashMap<>() { { put("101", "assets/student_101.csv"); /// ... } }; public static ArrayList<Subject> loadStudentMarks(String filePath) throws Exception { ArrayList<Subject> subjects = new ArrayList<>(); BufferedReader reader = new BufferedReader(new FileReader(filePath)); reader.readLine(); String line; while ((line = reader.readLine()) != null) { String[] parts = line.split(","); subjects.add(new Subject(parts[0], Float.parseFloat(parts[1]), Integer.parseInt(parts[2]))); } reader.close(); return subjects; } } Subject.java class Subject { Subject() { } Subject(String name, float mark, int credit) { this.name = name; this.mark = mark; this.credit = credit; } String name; float mark; int credit; double getCGPA(GradingPointSystem system) { return system.getGP(this); } }