读对象数据流 Java 出错代码

import java.io.*;
import java.util.*;
public class Test{
 public static void main(String[] args) throws IOException{
/* Date d=new Date();
 
 FileOutputStream f=new FileOutputStream("date.txt");
 ObjectOutputStream s=new ObjectOutputStream(f);
 try{
  s.writeObject(d);
  s.close();
 }catch(IOException e){
  e.printStackTrace();
 }
 */
 
 Date d=null;
 FileInputStream f=new FileInputStream("date.ser");
 ObjectInputStream s=new ObjectInputStream(f);
 try{
  d = (Date)s.readObject(d);//此处错误提示The method readObject() in the type   s.close();
 }catch(IOException e){      //ObjectInputStream is not applicable for the arguments (Date)

  e.printStackTrace();
 }
  System.out.println("date  at"+d);
 }
}