CODEWITHSUNDEEP
java
A M A
A M A

Reputation: 45

calling interface function that is not implemented in java

I am having trouble understanding a code that is using an interface function but i don't seem to find the implementation for it. Is it possible to call an unimplemented interface function? The code is below, The class that calls the unimplemented function combineResults:

public final class Parallel { 
 public static <T> T For(int start, int end, 
   ParallelForDelegate<T> delegate, T input) { 
  T res = null; 
  for (int i = start; i < end; i++) { 
   res = delegate.combineResults(res, delegate.delegate(i, input)); 
  } 
  return res; 
 } 
 }

The interface:

public  interface  ParallelForDelegate<T> { 
 public  T delegate(int i, T input); 

 public  T combineResults(T result1, T result2); 
}

Reference: https://www.programcreek.com/java-api-examples/index.php?source_dir=SecugenPlugin-master/src/sourceafis/simple/Fingerprint.java#

Upvotes: 2

Views: 834

Answers (2)

Ramesh
Ramesh

Reputation: 340

In the method

public static T For(int start, int end, ParallelForDelegate delegate, T input)

of Parallel class you are taking ParallelForDelegate as a reference, so, you can call methods of ParallelForDelegate Interface. the key thing is you have to pass implementation class object of ParallelForDelegate interface when you call For (-,-,-,-) method. So,

delegate.combineResults(res, delegate.delegate(i, input));

calls, that implementation class method at runtime.

Upvotes: 1

HBo
HBo

Reputation: 633

There has to be an implementation somewhere, but sometimes you can have a hard time finding it, because of various factories, dependecy injections, 'on-the-fly' building, ... mecanisms

On complex APIs like Hibernate, it can be tedious. However, the interface is supposed to give you enough details on its usage so you don't actually have to know how it's implemented.

Upvotes: 1

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