课后思考及问题
1：老师能深入细致的讲讲JAVA怎么实现序列化的嘛？比如：一个对象怎么一步步神奇的变成一个字节数组的？对象中的属性、属性值、方法、以及此对象的信息怎么变成一个字节数组的？
2：我们知道对象是通过在 ObjectInputStream 上调用 readObject() 方法进行反序列化的，这个方法其实是一个神奇的构造器，它可以将类路径上几乎所有实现了 Serializable 接口的对象都实例化。
这个神奇的构造器的实现原理是啥？一个字节数组他怎么将其转换为一个对象的？很好奇，他知道字节数组多少位表示啥意思？然后一段一段的取，一段的翻译嘛？老师给讲讲呗？
老师深入讲一下原理实现细节，API式的讲解不过瘾，和老师要深入理解的风格也不符呀😄

老师，我试着写了一下这个问题的代码，但是发现Singleton 序列化和反序列化后会产生两个instance, 这个问题怎么解？以下是我的代码，
'''
...
public static void serializeMe() {
        try {
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("SingletonData.txt"));
            oos.writeObject(Singleton.getInstance());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Object deSerializeMe() {
        Object obj = null;
        try {
            ObjectInputStream ois = new ObjectInputStream(new FileInputStream("SingletonData.txt"));
            obj = ois.readObject();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
        return obj;
    }

    private static class Singleton implements Serializable {
        int i;
        private static Singleton instance = null;
        private Singleton() {
            System.out.println("Executing constructor");
            i = 1;
        }

        // key change here !!!
        private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
            System.out.println("readObject before [i=" + i + "]");
            ois.defaultReadObject();
            instance = this; // After de-serialization, two objects of 'Singleton' class are created.
            System.out.println("readObject after [i=" + i + "]");
        }

        // thread unsafe here, don't care
        public static Singleton getInstance() {
            if (instance == null) {
                instance = new Singleton();
            }
            System.out.println("An instance is returned");
            return instance;
        }

        // readResolve() is usually called after readObject()
        public Object readResolve() {
            System.out.println("Executing readResolve");
            return instance;
        }

        @Override
        public String toString() {
            return "Singleton [i=" + i + "]";
        }
    }
'''