为什么在尝试将子类读入父类变量时没有错误？我认为在创建一个已经被编译器读取的对象之前 serialVersionUID 两个类（变量类和已读取的类）的 serialVersionUID 不相等 InvalidClassException 被抛出。我也是 A 类和 B 班级有相同的 serialVersionUID ?

import java.io.*;

class A  {}

class B extends A implements Serializable {}

public class Test
{
    public static void main(String[] args) throws IOException, ClassNotFoundException
    {
        FileOutputStream fileOutputStream = new FileOutputStream("b.bin");
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
        B b1 = new B();
        objectOutputStream.writeObject(b1);
        objectOutputStream.close();

        FileInputStream fileInputStream = new FileInputStream("b.bin");
        ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
        A a1 = (A) objectInputStream.readObject(); // why I don't have an InvalidClass Exception here
        objectInputStream.close();
    }
}