ফাইল আই/ও (File I/O)

import java.io.FileWriter;
import java.io.PrintWriter;
import java.io.IOException;

public class Main {
    public static void main(String[] args) {
        // Method 1: PrintWriter — easy and familiar
        try (PrintWriter writer = new PrintWriter(new FileWriter("scores.txt"))) {
            writer.println("=== High Scores ===");
            writer.println("Anika: 950");
            writer.println("Rafi: 870");
            writer.println("Sadia: 920");
            writer.printf("Average: %.1f%n", (950 + 870 + 920) / 3.0);
            System.out.println("File written successfully!");
        } catch (IOException e) {
            System.out.println("Error writing file: " + e.getMessage());
        }

        // Method 2: Appending to an existing file (true = append mode)
        try (PrintWriter appender = new PrintWriter(new FileWriter("scores.txt", true))) {
            appender.println("Tariq: 990");  // added to the end
            System.out.println("Appended successfully!");
        } catch (IOException e) {
            System.out.println("Error appending: " + e.getMessage());
        }
    }
}

File written successfully!
Appended successfully!

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // First, let's check if the file exists
        File file = new File("scores.txt");
        System.out.println("File exists: " + file.exists());
        System.out.println("File name: " + file.getName());
        System.out.println("Absolute path: " + file.getAbsolutePath());

        System.out.println("---");

        // Read the file line by line with Scanner
        try (Scanner reader = new Scanner(file)) {
            int lineNumber = 1;
            while (reader.hasNextLine()) {
                String line = reader.nextLine();
                System.out.println(lineNumber + ": " + line);
                lineNumber++;
            }
        } catch (FileNotFoundException e) {
            System.out.println("File not found: " + e.getMessage());
        }
    }
}

File exists: true
File name: scores.txt
Absolute path: /path/to/scores.txt
---
1: === High Scores ===
2: Anika: 950
3: Rafi: 870
4: Sadia: 920
5: Average: 913.3
6: Tariq: 990

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.PrintWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        // First, create a sample CSV file
        try (PrintWriter w = new PrintWriter(new FileWriter("students.csv"))) {
            w.println("Name,Grade,Score");
            w.println("Anika,A,95");
            w.println("Rafi,B,83");
            w.println("Sadia,A,91");
            w.println("Tariq,C,74");
        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
            return;
        }

        // Read and parse the CSV with BufferedReader
        ArrayList<String> honorRoll = new ArrayList<>();

        try (BufferedReader br = new BufferedReader(new FileReader("students.csv"))) {
            String header = br.readLine();  // skip header row
            System.out.println("Header: " + header);
            System.out.println("---");

            String line;
            while ((line = br.readLine()) != null) {
                String[] parts = line.split(",");
                String name = parts[0];
                String grade = parts[1];
                int score = Integer.parseInt(parts[2]);

                System.out.printf("%s got a %s (%d)%n", name, grade, score);

                if (score >= 90) {
                    honorRoll.add(name);
                }
            }

            System.out.println("\nHonor Roll: " + honorRoll);
        } catch (IOException e) {
            System.out.println("Error reading: " + e.getMessage());
        }
    }
}

Header: Name,Grade,Score
---
Alice got a A (95)
Bob got a B (83)
Charlie got a A (91)
Diana got a C (74)

Honor Roll: [Anika, Sadia]