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Java Forum / First Aid / June 2008Throwing Close To the Edge: a micro quiz for newbies.
Here are some questions for newbies on the throws clause you apply to a method. The quiz consists of 9 true-false questions. This is open-book. You can read the JLS or perform compiler experiments. Post your answers if you are feeling brave. Class2 extends Class1. Class2.method overrides Class1.method. 1. is it ok for Class1.method to have some throws that Class2.method does not:? 2. is it ok for Class2.method to have some throws that Class1.method does not? 3. is it ok for Class1.method to have throw IOException while Class2.method throws EOFException (a subclass of IOException)? 4. is it ok for Class2.method to have throw IOException while Class1.method throws EOFException? Class2 Implements Interface1. Class2.method implements Interface1.method 5. is it ok for Interface1.method to have some throws that Class2.method does not:? 6. is it ok for Class2.method to have some throws that Interface1.method does not? 7. is it ok for Interface1.method to have throw IOException while Class2.method throws EOFException (a subclass of IOException)? 8. is it ok for Class2.method to have throw IOException while Interface1.method throws EOFException? Interface2 extends Interface1. 9. is it ok for Interface2 to have an method named the same as in Interface1?  SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Roedy Green schreef: | Here are some questions for newbies on the throws clause you apply to | a method. The quiz consists of 9 true-false questions. This is | open-book. You can read the JLS or perform compiler experiments. | Post your answers if you are feeling brave. Off the top of my head: | Class2 extends Class1. Class2.method overrides Class1.method. | | 1. is it ok for Class1.method to have some throws that Class2.method | does not:? Yes, overriding signatures have to follow Liskov, which in this case means you can leave out Exceptions (e.g. FileWriter does so). | 2. is it ok for Class2.method to have some throws that Class1.method | does not? Nope, for the same reason (might be that they make exceptions for RuntimeException) | 3. is it ok for Class1.method to have throw IOException while | Class2.method throws EOFException (a subclass of IOException)? Yes, for the same reason: the overriding method can be more explicit in the Exceptions it throws. | 4. is it ok for Class2.method to have throw IOException while | Class1.method throws EOFException? Nope. All Liskov. | Class2 Implements Interface1. Class2.method implements | Interface1.method | | 5. is it ok for Interface1.method to have some throws that | Class2.method does not:? Yes. Liskov. | 6. is it ok for Class2.method to have some throws that | Interface1.method does not? No. Liskov. | 7. is it ok for Interface1.method to have throw IOException while | Class2.method throws EOFException (a subclass of IOException)? Yes. Liskov. | 8. is it ok for Class2.method to have throw IOException while | Interface1.method throws EOFException? No. Liskov. | Interface2 extends Interface1. | | 9. is it ok for Interface2 to have an method named the same as in | Interface1? What do you mean ‘named’? Same signature? Then I’d guess no, otherwise: yes, overloading is allowed in Java. H. - -- Hendrik Maryns http://tcl.sfs.uni-tuebingen.de/~hendrik/ ================== http://aouw.org Ask smart questions, get good answers: http://www.catb.org/~esr/faqs/smart-questions.html On Fri, 27 Jun 2008 06:06:57 GMT, Roedy Green <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted someone who said : >3. is it ok for Class1.method to have throw IOException while >Class2.method throws EOFException (a subclass of IOException)? To clarify the question. I mean that Class1.method has a throws declaration for IOException while Class2.method has a declaration for throws EOFException. Obviously a method may throw an EOFException of it has declared a throws IOException. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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