带继承的序列化(Java)

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我正在学习序列化和继承,并且我不了解谁在反序列化过程中调用了no-arg构造函数.超类A不实现Serializable,而子类B扩展A实现Serializable.

超类A

public class A {

    int i;

    public A(int i) 
    {
        this.i = i;
    }

    public A()
    {
        i = 50;
        System.out.println("A's class constructor called");
    }  
}

B类

import java.io.Serializable;

public class B extends A implements Serializable {

    int j;

    // parameterized constructor
    public B(int i,int j) 
    {
        super(i);
        this.j = j;
    }
}

驾驶员等级

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Test {

    public static void main(String[] args) throws Exception {

        B b1 = new B(10,20);

        System.out.println("i = " + b1.i);
        System.out.println("j = " + b1.j);

        // Serializing B's(subclass) object 

        //Saving of object in a file
        FileOutputStream fos = new FileOutputStream("abc.ser");
        ObjectOutputStream oos = new ObjectOutputStream(fos);

        // Method for serialization of B's class object
        oos.writeObject(b1);

        // closing streams
        oos.close();
        fos.close();

        System.out.println("Object has been serialized");

        // De-Serializing B's(subclass) object 

        // Reading the object from a file
        FileInputStream fis = new FileInputStream("abc.ser");
        ObjectInputStream ois = new ObjectInputStream(fis);

        // Method for de-serialization of B's class object
        B b2 = (B)ois.readObject();  // The A() constructor is called here

        // closing streams
        ois.close();
        fis.close();

        System.out.println("Object has been deserialized");

        System.out.println("i = " + b2.i);
        System.out.println("j = " + b2.j);
    }
}

如果删除A()构造函数,则会收到InvalidClassException.我看到在创建b2对象时调用了A(),但我不明白为什么在此语句中调用此A()以及调用它的人.

创建b1对象时,将调用B(int i,int j)构造函数以及A(int i)构造函数.这很容易理解.但是我不明白为什么在创建b2对象时调用A()构造函数.

解决方法:

从Serializable JavaDocs开始：

To allow subtypes of non-serializable classes to be serialized, the subtype may assume responsibility for saving and restoring the state of the supertype’s public, protected, and (if accessible) package fields. The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class’s state. It is an error to declare a class Serializable if this is not the case. The error will be detected at runtime.

现在您的问题：

If I delete the A() constructor I get the InvalidClassException. I see that A() is called when the b2 object is created but I don’t understand why this A() is called at this statement and who called it.

串行化机制通过反射调用A()构造函数.特别是通过ObjectStreamClass从ObjectInputStream获得.

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