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INterface should have implemetation

 
sanjey asok
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here ExecutorService is an interface and Executors.newFixedThreadPool(NTHREDS); return a n intreface ,how it is possible?,an interface should have implementation class ?
 
saurav sarkar
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Hi Sanjey,

Here actually the type of reference is an interface but it is actually
poniting to an implementation of ExecutorService.

The method Executors.newFixedThreadPool(NTHREDS); actually
returns an implementation of ExecutorService.

cheers,
Saurav
 
Jesper de Jong
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It's perfectly ok to make a variable of a type that is an interface refer to an object of a class that implements the interface. For example, you can write:

Note that List is an interface, and ArrayList is a class that implements the List interface. The rest of the program, that uses list, only needs to know that it is an object of a class that implements List; it doesn't need to know that it's actually an ArrayList (or some other implementation such as LinkedList).

Likewise, the method Executors.newFixedThreadPool returns an object that's an instance of a class that implements the ExecutorService interface. You don't need to know what that exact class is to be able to use the ExecutorService.
 
It is sorta covered in the JavaRanch Style Guide.
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