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Generic Type java

 
Ranch Hand
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iI have the snippet of following code

Which method header can be inserted at (1) so that the program compiles and runs
without errors?
Select the one correct answer.
(a) static <E extends CharSequence> Collection<? extends CharSequence>
delete4LetterWords(Collection<E> words)
(b) static <E extends CharSequence> List<E>
delete4LetterWords(Collection<E> words)
(c) static <E extends CharSequence> Collection<E>
delete4LetterWords(Collection<? extends CharSequence> words)
(d) static <E extends CharSequence> List<E>
delete4LetterWords(Collection<? extends CharSequence> words)
(e) static <E extends CharSequence> Collection<E>
delete4LetterWords(Collection<E> words)
(f) public <E super CharSequence> Collection<E>
delete4LetterWords(Collection<E> words)
the correct answer is (e)
please someone how telle me why the ather suggestion are not true i found a  confusion betwenn them to specify the correct answer
 
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This is not allowed because resultList on line 4 expects a return type of Collection<String>, and this method returns a Collection<? extends CharSequence>.

This is not allowed because permittedWords on line 8 is a Collection<String>, which you can't return if the return type is a List<String>.

This is not allowed because the loop variable word on line 9 expects String, but the words parameter is a Collection<? extends CharSequence>, meaning the elements are not necessarily String.

This is not allowed for the same reason as option b): You can't return a Collection if the return type is a List.

This is allowed.

This is not allowed because the length() method on line 10 is defined for CharSequence, and E is not necessarily CharSequence, it could be Object.

By the way, I assumed that the public keyword in the last option was supposed to be the static keyword.
 
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