2 Replies Latest reply on Mar 24, 2011 9:48 AM by 849958

    Chaining tasks using generics

      Hi everyone,

      I am trying to create an API for chaining tasks.

      First, I designed a very simple interface defining a task:

      public interface Task<U, V> {
      U execute(V input);

      Where V is the input type and U the output type of the task.

      What I whish to create is a Chain class that would chain a list of Tasks.

      For instance, I would like to exexute: Task1<TypeA, TypeB> -> Task2<TypeB, TypeC> -> Task3<TypeC, TypeD>

      This Chain class would thus be a Task<TypeA, TypeD>.

      So I wrote this code, which does not compile :

      public class Chain<U, V> implements Task<U, V>{
      List<Task<?, ?>> taskList;

      public Chain() {
      taskList = new LinkedList<Task<?, ?>>();

      public U execute(V input) {
      V currentInput = input;
      U output = null;
      for (Task<?, ?> task : taskList) {
      output = task.execute(currentInput); // Compile error because currentInput is of type V and output of type U
      currentInput = output; // Compile error as well

      return output;

      // Other methods to add and remove tasks in the list


      I do understand why it cannot compile but I have no idea how I could implement something that works and answers my problem.

      Has anyone ever faced this kind of problem?

      Kind regards,