User user = new User();

Class c = Class.forName(subClassName);

User user = (User)c.newInstance();// 不带参数

  Constructor con = c.getConstructor(String.class);
User user = (User) con.newInstance("name");

public Object getNewObject(String className) throws ClassNotFoundException, InstantiationException, IllegalAccessException { 
    //class.forName（类的全路径）、实例对象.class(属性)、实例对象getClass(),这三种方式都能得到class 
    Class tClass=Class.forName(className); 
    Object tObject=tClass.newInstance(); 
    return tObject; 
     
  } 

User user1 = new User(1,"dan");
  User user2 = null;
  user2 = (User) user1.clone();

import java.io.ObjectOutputStream;   
import java.io.ObjectInputStream;   
import java.io.FileInputStream;   
import java.io.FileOutputStream;   
import java.util.Date;   
import java.lang.management.*;   
public class Test {   
  
  
  
  //序列化对象到文件   
  public static void serialize(String fileName){   
    try  
    {   
      //创建一个对象输出流，讲对象输出到文件   
      ObjectOutputStream out=new ObjectOutputStream(new FileOutputStream(fileName));   
  
      UserInfo user=new UserInfo("renyanwei","888888",20);   
      out.writeObject(user); //序列化一个会员对象   
  
      out.close();   
    }   
    catch (Exception x)   
    {   
      System.out.println(x.toString());   
    }   
       
  }   
  //从文件反序列化到对象   
  public static void deserialize(String fileName){   
    try  
    {   
      //创建一个对象输入流，从文件读取对象   
      ObjectInputStream in=new ObjectInputStream(new FileInputStream(fileName));   
  
      //读取UserInfo对象并调用它的toString()方法   
      UserInfo user=(UserInfo)(in.readObject());        
      System.out.println(user.toString());   
  
      in.close();   
    }   
    catch (Exception x)   
    {   
      System.out.println(x.toString());   
    }   
       
  }   
  
  public static void main(String[] args) {     
  
    serialize("D:\\test.txt");   
    System.out.println("序列化完毕");   
       
    deserialize("D:\\test.txt");   
    System.out.println("反序列化完毕");   
  }   
  
}