Rice University - Comp 212 - Intermediate Programming

Spring 2002

Lecture #07 - Using "helper" methods

2. Composite Pattern (cont.)

Recall UML diagram illustrating the general composite pattern.

Using Helpers:

In many situations, an operation may call on "helper" operations on the sub-components to carry out the task.  The coding pattern for an  operation that requires a helper is as follows.

class Composite extends AComponent {
    // fields and sub-components.

    public Object doTask (Object input) {
      // Process the input parameter and the data fields to obtain a temporary result needed by the sub-components to help complete the task:
        Object temp = process (data fields, input);

      // Pass the temporary result to each of the sub-components asking each of them to "help" complete the task:
        Object pr1 = _part1.helpDoTask (temp); // partial result 1.
        Object pr2 = _part2.helpDoTask (temp);
        // etc...
        Object prN = _partN.helpDoTask (temp);

        // Reassemble the partial results computed by the sub-components to obtain the final result:
        return putTogether (pr1, pr2, ..., prN);
    }

    protected Object helpDoTask (Object input) {
      // Process the input parameter and the data fields to obtain a temporary result needed by the sub-components to help complete the task:
        Object temp = processPartial (data fields, input);

      // Pass the temporary result to each of the sub-components asking each of them to "help" complete the task:
        Object pr1 = _part1.helpDoTask (temp); // partial result 1.
        Object pr2 = _part2.helpDoTask (temp);
        // etc...
        Object prN = _partN.helpDoTask (temp);

        // Reassemble the partial results computed by the sub-components to obtain the final result:
        return putTogetherPartial (pr1, pr2, ..., prN);
    }
}

class Basic extends AComponent {
    // fields

    public Object doTask (Object input) {
      // Process the input parameter and the data fields to obtain the result:
        return simpleProcess (data fields, input);
    }

    protected Object helpDoTask (Object input) {
      // Process the input parameter and the data fields to obtain the result:
        return simpleProcessPartial (data fields, input);
    }
}