Java Serialization Example in Java

Introduction

Serialization converts a Java object into a byte stream for storage or network transfer. Deserialization reconstructs the object from that stream.

Example Program

import java.io.*;

class Student implements Serializable {
    private static final long serialVersionUID = 1L;
    private int id;
    private String name;
    private transient String password; // not written to file

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

    @Override
    public String toString() {
        return "Student{id=" + id + ", name='" + name + "', password='" + password + "'}";
    }
}

public class SerializationDemo {
    public static void main(String[] args) {
        String file = "student.ser";

        Student original = new Student(101, "Thiyagaraaj", "secret123");

        // Serialize
        try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file))) {
            out.writeObject(original);
            System.out.println("Serialized: " + original);
        } catch (IOException e) {
            e.printStackTrace();
        }

        // Deserialize
        try (ObjectInputStream in = new ObjectInputStream(new FileInputStream(file))) {
            Student restored = (Student) in.readObject();
            System.out.println("Deserialized: " + restored);
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Sample Output

Serialized: Student{id=101, name='Thiyagaraaj', password='secret123'}
Deserialized: Student{id=101, name='Thiyagaraaj', password='null'}

How It Works

1. The class implements Serializable (a marker interface).
2. ObjectOutputStream.writeObject() writes the object graph to a file.
3. ObjectInputStream.readObject() reads it back.
4. The transient password field is skipped during serialization, so it becomes null after restore.

Best Practices

• Declare serialVersionUID for maintainable serializable classes.
• Mark sensitive fields as transient.
• Consider JSON or protocol buffers for cross-language persistence instead of Java-native serialization.

Common Mistakes

• Attempting to serialize a class that does not implement Serializable.
• Changing class structure without managing version compatibility.