反序列化时，并没有强制转换，为什么还能正常打印结果

package com.IOUtil.io;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

public class ObjectSeriaDemo01 {

public static void main(String[] args) throws IOException, ClassNotFoundException {

/*

//对象的序列化

String file = "demo\\obj.dat";

ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file));

Student stu = new Student("012", "王栋祥", 22);

oos.writeObject(stu);

*/

//对象的反序列化

String file = "demo\\obj.dat";

ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file));

//ois.readObject();

System.out.println(ois.readObject());

}

}