Advanced Java Day 2: File I/O and Serialization

Goal of this Day

Today you will learn:

• Reading and writing files using FileReader, BufferedReader, FileWriter, and BufferedWriter
• Object serialization with the Serializable interface
• Handling large files efficiently

By the end, you will be able to read and write files and serialize objects in Java.

Step 1: Writing Files

Use BufferedWriter with FileWriter for efficient writing.

import java.io.*;

try(BufferedWriter writer = new BufferedWriter(new FileWriter("data.txt"))) {
    writer.write("Hello Advanced Java!");
} catch(IOException e) {
    e.printStackTrace();
}

Step 2: Reading Files

Use BufferedReader with FileReader for efficient reading.

import java.io.*;

try(BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) {
    String line;
    while((line = reader.readLine()) != null){
        System.out.println(line);
    }
} catch(IOException e) {
    e.printStackTrace();
}

Step 3: Object Serialization

Serialization allows you to save objects to a file and read them back.

import java.io.*;

class Person implements Serializable {
    private String name;
    private int age;

    public Person(String name, int age){
        this.name = name;
        this.age = age;
    }

    public String toString() {
        return name + " is " + age + " years old.";
    }
}

public class SerializeExample {
    public static void main(String[] args) {
        Person person = new Person("Alice", 25);

        // Serialize
        try(ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("person.dat"))) {
            oos.writeObject(person);
        } catch(IOException e) {
            e.printStackTrace();
        }

        // Deserialize
        try(ObjectInputStream ois = new ObjectInputStream(new FileInputStream("person.dat"))) {
            Person readPerson = (Person) ois.readObject();
            System.out.println(readPerson);
        } catch(IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Practice

import java.io.*;

try(BufferedWriter writer = new BufferedWriter(new FileWriter("data.txt"))) {
    writer.write("Hello Advanced Java!");
}

try(BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) {
    String line;
    while((line = reader.readLine()) != null){
        System.out.println(line);
    }
}

Exercise

Serialize an object to a file and read it back.

Steps:

• Create a class implementing Serializable
• Write an object of the class to a file using ObjectOutputStream
• Read the object back using ObjectInputStream
• Print the object to verify

Example:

import java.io.*;

class Student implements Serializable {
    private String name;
    private int id;

    public Student(String name, int id){
        this.name = name;
        this.id = id;
    }

    public String toString() {
        return "Student: " + name + ", ID: " + id;
    }
}

public class StudentSerialize {
    public static void main(String[] args) {
        Student s = new Student("Bob", 101);

        // Serialize
        try(ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.dat"))) {
            oos.writeObject(s);
        } catch(IOException e) {
            e.printStackTrace();
        }

        // Deserialize
        try(ObjectInputStream ois = new ObjectInputStream(new FileInputStream("student.dat"))) {
            Student readStudent = (Student) ois.readObject();
            System.out.println(readStudent);
        } catch(IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}