They do this usually by generating a warning if you do not have this field. Note that many classes are serializable; any time you extend a class that is serializable, that class also counts. For ...

定义一个类显示指定 serialVersionUID 的值进行序列化，然后修改 serialVersionUID 的值，再进行反序列化，此时会抛 java.io.InvalidClassException 异常，这证明 serialVersionUID 的版本信息被隐式记录在流中了，但是通过查看序列化后的二进制文件，并没有存储 serialVersionUID 的值。