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Easy Learn Java: Programming Articles, Examples and Tips - Page 110


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In Ukraine first day of week is Monday but not Sunday

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Question: In Ukraine first day of week is Monday but not Sunday

By defaults in the calendar object obtained with locale ua_UA getFirstDayOfWeek
() function return SUNDAY as a first week day... Java version is 1.3.1_01

Answer: Yes indeed, according to this list:
http://www.pjh2.de/datetime/weeknumber/wnd.php
the first day in Ukraine is Monday. For those who does not know will say that in many countries Sunday or even Saturday is first day, for example in Egypt - Saturday and in Argentina and Brasil - Sunday...
It was a bug since according to ISO 8601 in all European countries a week starts with Monday...
I know that with Hungarian calendar was the same bug... In latest 1.4.1 and beyond the bug is fixed.

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40 comments | Printer Friendly Page  Send to a Friend | Score: 4
Posted by jalex on Monday, December 01, 2003 (00:00:00) (4541 reads)

When do I to choose an abstract class over an interface?

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Question: When do I to choose an abstract class over an interface?

Answer: Choosing interfaces and abstract classes is not an either/or proposition...

"Often in a design, you want the base class to present only an interface for its derived classes. That is, you don't want anyone to actually create an object of the base class, only to upcast to it so that its interface can be used. This is accomplished by making that class abstract using the abstract keyword. If anyone tries to make an object of an abstract class, the compiler prevents them. This is a tool to enforce a particular design.

You can also use the abstract keyword to describe a method that hasn't been implemented yet-as a stub indicating "here is an interface function for all types inherited from this class, but at this point I don't have any implementation for it." An abstract method may be created only inside an abstract class. When the class is inherited, that method must be implemented, or the inheriting class becomes abstract as well. Creating an abstract method allows you to put a method in an interface without being forced to provide a possibly meaningless body of code for that method.

The interface keyword takes the concept of an abstract class one step further by preventing any function definitions at all. The interface is a very handy and commonly used tool, as it provides the perfect separation of interface and implementation. In addition, you can combine many interfaces together, if you wish, whereas inheriting from multiple regular classes or abstract classes is not possible."

from "Thinking in Java", http://javafaq.nu/java/book/Chapter01.shtml#Heading29
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9 comments | Printer Friendly Page  Send to a Friend | Score: 3.33
Posted by jalex on Friday, November 14, 2003 (00:00:00) (4360 reads)

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