java对象序列化与反序列化中的构造方法问题

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


public class main {
	public static void main(String[] args)throws IOException, ClassNotFoundException{
		ObjectOutputStream oos=new ObjectOutputStream(
				new FileOutputStream("employee.dat"));
		Foo2 foo2=new Foo2();
		oos.writeObject(foo2);
		oos.flush();
		oos.close();
		ObjectInputStream ois=new ObjectInputStream(
				new FileInputStream("employee.dat"));
		Foo2 foo21= (Foo2)ois.readObject();
		
		System.out.println(foo21);
		ois.close();
	}
}
class Foo {
	public Foo(){
		System.out.println("foo...");
	}
}
class Foo1 extends Foo implements Serializable{
	public Foo1(){
		System.out.println("foo1...");
	}
}

class Foo2 extends Foo1{
	public Foo2(){
		System.out.println("foo2...");
	}
}
import java.io.FileInputStream;