16.8. Handling Inheritance

If a superclass is not serializable, its fields will not be serialized.

When you create a class in Java, it can extend another class (a superclass). If the superclass does not implement the Serializable interface, any fields (variables) defined in that superclass will not be included when an object of the subclass is serialized. This means that when you convert the subclass object into a byte stream and later reconstruct it (deserialize), those fields from the superclass are essentially lost.

Think of a vehicle that has a mandatory inspection before it's allowed on the road. If the vehicle is not inspected, it cannot be registered, and all the features like the engine and wheels can't be considered valid. Similarly, if a superclass isn’t marked as serializable, its properties just won’t be part of the serialization process.

Example:

class Person {
    String nationality = "Indian";
}
class Employee extends Person implements Serializable {
    int id;
}

• On deserialization, nationality will not retain its state.

In the example, the Person class represents a general entity with a nationality. It does not implement the Serializable interface, so when you create an Employee object that extends Person, even though Employee is serializable, the nationality field from Person will not be serialized. When you deserialize an Employee, the nationality field will not have the value "Indian" anymore; it will simply be null or the default value for that field type.

Imagine an employee who comes from a country (like nationality), but when you move their records to a new system (deserialization), you only get their employee ID without any information about their nationality since that part was never recorded. It’s like giving someone a suitcase but forgetting to pack their important travel documents inside.

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