Does serialization need a native mechanism?

Question

I created a Class with a private constructor having one parameter which initializes a private attribute.

An object of this class can be serialized and deserialized properly with the ObjectInputStream/ObjectOutputStream class.

This isn't possible with json serialization/deserialization because the class has no getters, no setters and no public default constructor.

So I am wondering how this works. I know a Java method can access the private elements of an object via introspection, but with output stream deserialization, how can Java successfully instantiate the object without a default constructor it doesn't know the value of the parameters used to create it?

Here is the code for which I don't understand the mechanism:

public class Main implements Serializable {
    private int number;

    private Main(int number){
        this.number = number;
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Main main = new Main(12);
        ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("file.bin"));
        outputStream.writeObject(main);
        outputStream.close();

        ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("file.bin"));
        Main main2 = (Main) objectInputStream.readObject();
        objectInputStream.close();
        System.out.println(main2.number); // 12
    }
}