Generic functional interface

Question

I'm facing with some lambda problem.
I'm trying to use lambda expression and functional interface to create method accepting functional interface and some arguments and execute that function.

Here is my code:

@FunctionalInterface
interface TwoArgumentFunction {
    public <T, K, V> T doJob(K arg1, V arg2);
} //I know I've ommited return value in that case


class SomeClass {
<T, K, V> T runLongAction(TwoArgumentFunction action, K arg1, V arg2){
    SwingWorker<T, Void> worker = new SwingWorker<T, Void>(){

        @Override
        protected T doInBackground() throws Exception {
            {... some code ... }
            return action.doJob(arg1, arg2);
        }
        @Override
        protected void done(){
            {... some code ... }
        }

    };
    worker.execute();
    try {
        return worker.get();
    } catch (InterruptedException | ExecutionException e) {
        {... some code ... }
    }
}


void mainInvoke(ArgType1 arg1, ArgType2 arg2){
    runLongAction((arg1, arg2) -> doSomething(arg1, arg2), arg1, arg2);
}

}

I've got error:

The method runLongAction(( arg1, arg2) -> {}, ArgType1, ArgType2) is undefined for the type SomeClass

I even tried cast lambda to TwoArgumentFunction but then I've got:

Illegal lambda expression: Method doJob of type TwoArgumentFunction is generic

Anonymouse class instead of lambda expression works fine and that's the simplest workaround I found.

Answer 1

Try that :

  @FunctionalInterface
  interface TwoArgumentFunction<T, K, V> {
     T doJob(K arg1, V arg2);
  } //I know I've ommited return value in that case

  public <T, K, V> T runLongAction(final TwoArgumentFunction<? extends T, ? super K, ? super V> action, final K arg1, final V arg2) {
    return action.doJob(arg1, arg2);
  }

  private void test() {
    final String a = "A";
    final Long b = 1L;
    this.runLongAction((ta, tb) -> {return 1;}, a, b);
  }

You were putting the generics on the method, while I putted it on the interface. And I also added ? super and ? extends (but this work without it).

In case you don't know it and if you need it, you can also put the type in the lambda :

this.runLongAction((String ta, Long tb) -> {return 1;}, a, b);

Answer 2

There is no need for you to create an interface that already exists in Java 8. You should use the 'BiFunction' interface, which has a method 'R apply(T t, U u))'.