I need a function that it receive a function by parameter that can be called inside

I want to do a function for execute any function received by parameter in intervals.
To explain myself better, I will give you an example.

I want to use this function for make calls to a rest client but, instead of do the call with a list with 10 elements, I want to can do 5 calls with 2 elements.

My problem is I don't want have to manage loops and intervals in all methods that I want call in intervals, I would like do something like this: Util.executeInIntervals (2 (interval), this.restClient.doPost(fullList) ); This method should do calls to this restClient in intervals as indicated below.

I have been able to this example class but the result isn't the correct:

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;

public class FunctionAsParameter {
  
  public static <T> void executeInIntervals(List<T> list, int interval, Function function) {
    // It's defined the num of interval
    final int INTERVAL = interval;

    int cont = 0;
    while(list.size() - cont > INTERVAL) {
      function.apply(list.subList(cont,cont + INTERVAL).toString());
      cont = cont + INTERVAL;
    }
    // The rest are processed
    function.apply(list.subList(cont,list.size()));
  }
}
class Main {
  public static void main(String[] args) {

    List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
    
    FunctionAsParameter.executeInIntervals(list, 2, value -> {
      // Here it would be the call to rest client with the sublist, not the full list 
      System.out.println(list);
      // This I would like remove but java indicates that the function can't be void
      return "";
    });
  }
}

Result:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Correct result would be:

[1, 2]
[3, 4]
[5, 6]
[7, 8]
[9, 10]

Thanks for advance.

Your callback ignores the parameter you pass into it and it is also unclear what the parameter should be (you call it once with a String and once with a List<T>).

You could try to fix your code like this:

import java.util.Arrays;
import java.util.List;
import java.util.function.Function;

public class FunctionAsParameter {
  
  public static <T> void executeInIntervals(List<T> list, int interval, Function<List<T>, String> function) {
    // It's defined the num of interval
    final int INTERVAL = interval;

    int cont = 0;
    while (list.size() - cont > INTERVAL) {
      function.apply(list.subList(cont, cont + INTERVAL));
      cont = cont + INTERVAL;
    }
    // The rest are processed
    function.apply(list.subList(cont, list.size()));
  }
}

class Main {
  public static void main(String[] args) {

    List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
    
    FunctionAsParameter.executeInIntervals(list, 2, value -> {
      System.out.println(value);
      return "";
    });
  }
}

If you want to remove that return ""; (because you don't use the return value of that function anyway) then Function is the wrong interface - you should use a Consumer:

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class ConsumerAsParameter {

    public static <T> void executeInIntervals(List<T> list, int interval, Consumer<List<T>> consumer) {
        // It's defined the num of interval
        final int INTERVAL = interval;

        int cont = 0;
        while (list.size() - cont > INTERVAL) {
            consumer.accept(list.subList(cont, cont + INTERVAL));
            cont = cont + INTERVAL;
        }
        // The rest are processed
        consumer.accept(list.subList(cont, list.size()));
    }
}

class Main {
    public static void main(String[] args) {

        List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

        ConsumerAsParameter.executeInIntervals(list, 2, value -> {
            System.out.println(value);
        });
    }
}

Note that in this simple example you could replace the executeInIntervals() call even further:

ConsumerAsParameter.executeInIntervals(list, 2, System.out::println);

For the example that you mention in a comment, the code could look like this:

ConsumerAsParameter.executeInIntervals(fullList, 2, this.restClient::doPost));