class AUtil {
public static String getStringA() {
return "A";
}
}
class ExtendedAUtil extends AUtil {
public static String getStringABCDE() {
return "ABCDE";
}
}
public class Main {
public static void main(String[] args) {
System.out.println(ExtendedAUtil.getStringA());
System.out.println(ExtendedAUtil.getStringABCDE());
}
}
Maybe it's better to add some runnable codes :)
Xeno Amess <xenoam...@gmail.com> 于2020年9月6日周日 下午10:05写道：
> Well sometimes we want to extend(or modify) some behaviors of one Util
> Class.That is why I don't want the constructor be private.
> For example, there be a AUtil:
>
> public class AUtil{
> public static String getStringA(){
> return "A";
> }
> }
>
> then some people need a function that returns "ABCDE".
> Actually "ABCDE" is useless for any other repos, so we can never pass the
> pr to put the getABCDE function to AUtil.
> And that people also need the getStringA function.
> So there be a way:
>
> public class ExtendedAUtil extends{
> public static String getStringABCDE(){
> return "ABCDE";
> }
> }
>
> In this way that people can use ExtendedAUtil as an extended AUtil.
> I admit that might be sugar and tricky, but it will help shorten the codes.
> BUT if we make the AUtil have only private constructor, then we cannot do
> such things, as class who have private constructors only cannot be extended.
>
> Melloware <melloware...@gmail.com> 于2020年9月6日周日 下午9:55写道：
>
>> That is why I love Lombok's @UtilityClass.
>>
>> https://projectlombok.org/features/experimental/UtilityClass
>>
>> It enforces a static class is truly static by making the constructor
>> private and throwing an exception, making sure all methods are static,
>> marking the class as Final etc.
>>
>>
>> On 9/6/2020 9:53 AM, Xeno Amess wrote:
>> >> Inheritance in Java on the static side is
>> > not the same as on the instance side
>> >
>> > Yep, I know it. It will not override but just, hiding.
>> > I admit it might confuse people sometimes.
>> >
>> >> subclassing a class that only
>> > provides static methods is no help.
>> >
>> > Well actually I personally use it for a shortcut or something.
>> > Of course we can do this by fork/wrap the static functions one by one,
>> but
>> > extending it directly can make the codes shorter.
>> >
>> > Gary Gregory <garydgreg...@gmail.com> 于2020年9月6日周日 下午9:48写道：
>> >
>> >> On Sun, Sep 6, 2020 at 9:44 AM Xeno Amess <xenoam...@gmail.com> wrote:
>> >>
>> >>> The idea behind not making *Util constructors private is that it makes
>> >>> people be able to extend that class.
>> >>> for example:
>> >>>
>> >>>
>> >>
>> https://github.com/apache/commons-lang/blob/master/src/main/java/org/apache/commons/lang3/StringUtils.java#L9627
>> >>
>> >>
>> >> I have not see a use case that requires instances of classes that only
>> >> provide static methods in a long time, like the Javadoc mentions, there
>> >> used to be JavaBean tools that needed this, and some UI builders IIRC,
>> but
>> >> I do not see a case of it today. Inheritance in Java on the static
>> side is
>> >> not the same as on the instance side, so subclassing a class that only
>> >> provides static methods is no help.
>> >>
>> >> Gary
>> >>
>> >>
>> >>> Gary Gregory <garydgreg...@gmail.com> 于2020年9月6日周日 下午9:39写道：
>> >>>
>> >>>> The idea behind making *Util constructors private is that it does not
>> >>> make
>> >>>> sense to instantiate a class that only has static methods.
>> >>>>
>> >>>> Gary
>> >>>>
>> >>>>
>> >>>> On Sun, Sep 6, 2020 at 12:49 AM Xeno Amess <xenoam...@gmail.com>
>> >> wrote:
>> >>>>> for example: can we make its constructor public instead of private?
>> >>>>>
>>
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