最近重新安装了Eclipse,在设计一个不继承任何类的类时,不会有任何warning,但在设计一个子类时,编译器经常提示“warning”,在网上查了很多资料终于搞定了这个问题:如下 测试提示:The serializable class FormatStr does not declare a static final serialVersionUID field of type long
static final long serialVersionUID = -3387516993124229948L;
这个有什么作用呢??
如果我这个子类一定要声明这个serialVersionUID 那应该怎样构造它的值呢??自己随便写一个long值就行了吗???
网上某人解答如下:
那与jdk的版本没关系吧.
那是Eclipse提供这个提示功能给你吧. 你点它warning的icon两下Eclipse就会自动给定. 如果你不喜欢,可以把它关掉,windows -> preferences -> compiler -> Error/Warnings-> Potential Programming problems 将Serializable class without serialVersionUID的warning改成ignore. 其实如果你没有考虑到兼容性问题时,那就把它关掉吧. 其实有这个功能是好的. 只要任何类别实作了Serializable这个介面, 如果没有加入serialVersionUID,Eclipse都会给你warning提示, 这个serialVersionUID为了让该类别Serializable後兼容. 考虑一下,如果今天你的类Serialized存到硬碟里, 可是後来你却更改了类别的field(增加或减少或改名). 当你Deserialize时,就会出现Exception.这样就会做成不兼容性的问题. 但当serialVersionUID相同时,它就会将不一样的field以type的预设值Deserialize. 这个可以避开不兼容性的问题. 至于你说内存的问题,我觉得没差多少吧.
在eclipse中,当一个类继承另一个类时,总是提示一个如下问题:
“The serializable class A does not declare a static final serialVersionUID field of type long” 然后我按照eclipse的建议(add default serial Version ID),增加如下代码: private static final long serialVersionUID = 1L;就没有错误提示了。 而且如果所定义的类没有继承其它类,也没有这个问题。
SUN官方网站解说摘要:
adcworks : Hi,
I develop with Eclipse IDE and am using the latest milestone that includes Java 5 syntax.
Since having upgraded, I get hundreds of the same warning for any class that extends another class with the following message:
Serializable class X does not declare a static final serialVersionUID field of type long.
I would like to know
a) Should I really ought to be doing something properly with this field, and if so, can you advise the best way to approach that.
b) Can I turn off these warnings. They are not in the Eclipse filter to exclude.
c) Is it safe to ignore them?
Thanks!
ehodges :
> a) Should I really ought to be doing something
> properly with this field, and if so, can you advise > the best way to approach that. Yes, if you actually serialize those objects. It can make version maintenance easier. > b) Can I turn off these warnings. They are not in the Eclipse filter to exclude. You turn them off on the Preferences | Compiler | Style page. It's the last item. > c) Is it safe to ignore them? Sure. You just won't have as much control over serialized versions.
ehodges :
>
Use the serialver.exe tool that comes with the jdk.
Or hit <ctrl>-1 in Eclipse. It will add a default or generated serial version ID for you. http://forum.java.sun.com/thread.jspa?threadID=581654&messageID=3501336 (Sun网页地址) |