一道关于java序列化的问题，看大家知多少————

问题先放在这里，稍后我会做出解答

已知类有Test和Test2，问两次主程序的输出结果是多少（SerializeUtil只是序列化的工具类）

类Test

public class Test implements Serializable{
    private static final long serialVersionUID = 1L;
    private int num;
    private transient String str;

    public Test(){
        this.num = 0xFFFF;
        this.str = "string";
    }

    public Test(int num, String str) {
        this.num = num;
        this.str = str;
    }

    @Override
    public String toString() {
        return num + ","+str;
    }
}

类Test2

public class Test2 implements Externalizable,Serializable{
    private static final long serialVersionUID = 1L;
    private int num;
    private transient String str;

    public Test2() {
        this.num = 0xFFFF;
        this.str = "hello";
    }

    public Test2(int num, String str) {
        this.num = num;
        this.str = str;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.write(num);
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        this.num = in.read();
    }


    @Override
    public String toString() {
        return num + ","+str;
    }
}

两个主程序：

    public static void main(String[] args) {
        Test test = new Test();
        File file = new File("d:/test.bin");
        SerializeUtil.writeObject(file,test);

        Test test2 = (Test) SerializeUtil.readObject(file);
        System.out.println(test);
        System.out.println(test2);
    }

    public static void main(String[] args) {
        Test2 test2 = new Test2();
        File file = new File("d:/test2.bin");

        SerializeUtil.writeObject(file,test2);
        Test2 t = (Test2) SerializeUtil.readObject(file);

        System.out.println(test2);
        System.out.println(t);
    }

附SerializeUtil的代码，可无视——

public class SerializeUtil {

    public static void writeObject(File file,Object object){
        FileOutputStream fileOutputStream = null;
        try {
            fileOutputStream = new FileOutputStream(file);
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
            objectOutputStream.writeObject(object);
            objectOutputStream.flush();
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(fileOutputStream!=null){
                try {
                    fileOutputStream.close();
                } catch (IOException e) {}
            }
        }
    }

    public static Object readObject(File file){
        FileInputStream fileInputStream = null;
        try {
            fileInputStream = new FileInputStream(file);
            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
            return objectInputStream.readObject();
        }catch (ClassNotFoundException|IOException e){
            e.printStackTrace();
        }finally {
            if(fileInputStream!=null){
                try {
                    fileInputStream.close();
                } catch (IOException e) {}
            }
        }
        return null;
    }

}

答案如下：

/*
第一个主程序：
65535,string
65535,null
第二个主程序：
65535,hello
255,hello
*/