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Is my definition of a generic method in Java ok?

Posted on 2011-09-14
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Here's my basic definition of a generic method. Is it acceptable?

Generic Method - a method in which type parameters appear within angled brackets, right before the return type. The code below is a generic method that uses an enhanced for loop to add array elements to a collection one by one. The third line of the code would not have compiled if the <T> at the beginning of the method signature was not there. That <T> made it possible for the array and the collection in the method parameter to be typed the same generic way, so that this method would be compatible with any object type.

static <T> void fromArrayToCollection(T[ ] a, Collection<T> c) {
     for (T o : a) {
        c.add(o); // adding an array element of type T
     }
}
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Question by:shampouya
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by:for_yan
ID: 36536407
Yes, this seems fine to me
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by:for_yan
ID: 36536412
if it compiles then it is fine
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by:for_yan
ID: 36536419
And it does compile fro me
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by:for_yan
ID: 36536436
Although my IDE suggest to replcae it withh Collection.addAll method, but this does not matter; once it compiles it measn it is correct
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by:shampouya
ID: 36536452
And the <T> after the word static is what turned this method into a generic method, right?
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by:for_yan
ID: 36536519
Yes, without that "T" in fromt of static compiler would not understdn what means T inside the mthod and in parameters
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by:for_yan
ID: 36536558
So this code compiles fine together with your method definition:

  
        Collection<String> cc = null;
        String [] cmcm = null;
        
            fromArrayToCollection(cmcm, cc);
        

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Author Comment

by:shampouya
ID: 36536584
Oh I know it compiles, correctly, I took it from the Oracle website. I was just wondering if my english was correct when I defined a generic method. And I was wondering if the <T> before the return type is what can turn a regular method into a generic method.
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by:for_yan
ID: 36536589

Aslo this compiles:

        Collection<Object> cc = null;
        String [] cmcm = null;

            fromArrayToCollection(cmcm, cc);

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but this does not:


Collection<String> cc = null;
        Object [] cmcm = null;

            fromArrayToCollection(cmcm, cc);

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This is in compliance with your previous
statements about covariance of arrays and collections
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Author Comment

by:shampouya
ID: 36536608
I'm confused and I'm not sure why you are telling me what compiles.That wasn't my question....
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by:for_yan
ID: 36536618
I just liked that your talks about covariance of arrays vs collections in previous question are nicely illustrated by this example
 
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Accepted Solution

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for_yan earned 500 total points
ID: 36536657
And about "T" in front:

Compiler has to account for any entity when it parses the code - each entity is either a class or variable name or something
which compiler should yunderstand.
If you don't put "T" in front - it will parse "T" inside the metghod definition - and will not know what it is - when it
saw "T" in front of static it understandts that it is a generic method and will
be able to recignize what is "T" when it parses the contents of the method.

By the way you can use almost arbitrary striung instead of "T" - I replaced "T" by "MyT" in all places and it also works - it is just a tradition to use "T" for "type"
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Author Closing Comment

by:shampouya
ID: 36536705
thanks
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