自定义继承类的序列化

Question

If want to write custom serialization method for derived class , Do I have to read and write base class fields again?

A implements Serializable
{
   field1,
   field2 etc

      private void readObject(ObjectInputStream inputStream) throws ClassNotFoundException, IOException
    {
      // read in field1
      //read in field2
    }

     private void writeObject(ObjectOutputStream outputStream) throws IOException
    {
       // write field1 to output stream
      //write field 2 to output stream
      }
}

Class B extends A
{
  field 3

      private void writeObject(ObjectOutputStream outputStream) throws IOException
    {
       //TODO : should contain only field 3 or field1,field2 and field 3?
    }

}

Answer 1

If you are calling writeObject on object of type B, it will not implicitly call the writeObject method in class A. You will have to call it yourself using super.writeObject(outStream) or else you can set all the three fields in the child method itself. In short, the writeObject function in B should contain all three fields in your case.

Answer 2

If you're overriding the method, you need to re-implement everything the parent class did as well.

As soon as you create a method in the derived class with the same signature as the parent class, it is overridden and the parent's method is no longer used for objects of type B.

Depending on your use case, you may want to consider using an abstract class.