以下验证了这一点：
package Serial;
import java.io.Serializable;
public class SuperC implements Serializable {//父类实现了序列化
int supervalue;
public SuperC(int supervalue) {
this.supervalue = supervalue;
}
public String toString() {
return "supervalue: "+supervalue;
}
}
public class SubC extends SuperC {//子类
int subvalue;
public SubC(int supervalue,int subvalue) {
super(supervalue);
this.subvalue=subvalue;
}
public String toString() {
return super.toString()+" sub: "+subvalue;
}
}
public class Test1 {
public static void main(String [] args){
SubC subc=new SubC(100,200);
FileInputStream in=null;
FileOutputStream out=null;
ObjectInputStream oin=null;
ObjectOutputStream oout=null;
try {
out = new FileOutputStream("Test1.txt");//子类序列化
oout = new ObjectOutputStream(out);
oout.writeObject(subc);
oout.close();
oout=null;
in = new FileInputStream("Test1.txt");
oin = new ObjectInputStream(in);
SubC subc2=(SubC)oin.readObject();//子类反序列化
System.out.println(subc2);
} catch (Exception ex){
ex.printStackTrace();
} finally{
…此处省略
}
}
}
运行结果如下：
supervalue: 100 sub: 200
可见子类成功的序列化/反序列化了。
怎管让子类实现序列化看起来是一件很简单的事情，但有的时候，往往我们不能够让父类实现Serializable接口，原因是有时候父类是抽象的（这并没有关系），并且父类不能够强制每个子类都拥有序列化的能力。换句话说父类设计的目的仅仅是为了被继承。
要为一个没有实现Serializable接口的父类，编写一个能够序列化的子类是一件很麻烦的事情。java docs中提到：
“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. ”
也就是说，要为一个没有实现Serializable接口的父类，编写一个能够序列化的子类要做两件事情：
其一、父类要有一个无参的constructor；
其二、子类要负责序列化（反序列化）父类的域。
我们将SuperC的Serializable接口去掉，而给SubC加上Serializable接口。运行后产生错误：
java.lang.Error: Unresolved compilation problem:
Serializable cannot be resolved or is not a valid superinterface
at Serial.SubC.
at Serial.Test1.main(Test1.java:19)
Exception in thread "main"
果真如docs中所说的一样，父类缺少无参构造函数是不行的。
接下来，按照docs中的建议我们改写这个例子：
public abstract class SuperC {
int supervalue;
public SuperC(int supervalue) {
this.supervalue = supervalue;
}
public SuperC(){}//增加一个无参的constructor
public String toString() {
return "supervalue: "+supervalue;
}
}
public class SubC extends SuperC implements Serializable {
int subvalue;
public SubC(int supervalue,int subvalue) {
super(supervalue);
this.subvalue=subvalue;
}
public String toString() {
return super.toString()+" sub: "+subvalue;
}
private void writeObject(java.io.ObjectOutputStream out)
throws IOException{
out.defaultWriteObject();//先序列化对象
out.writeInt(supervalue);//再序列化父类的域
}
pri
