Reducer.java

package org.softlang.company.features.template;

import org.softlang.company.model.*;

/**
 * Provide the template method "reduce" for querying values from companies.
 * The "reduce" method is configured with "visit" methods for all possible types.
 * There are also abstract methods for the result domain: "zero" and "append".
 */
public abstract class Reducer<R> {

    public R visit(Company c) {
        return zero();
    }

    public R visit(Department d) {
        return zero();
    }

    public R visit(Employee e) {
        return zero();
    }

    /**
     * @return the default (the algebraic unit) for the result type.
     */
    public abstract R zero();

    /**
     * Combine two query results.
     */
    public abstract R append(R x, R y);

    /**
     * Provide the template method "reduce" for querying values from companies.
     */
    public final R reduce(Company c) {
        R result = visit(c);
        for (Department d : c.getDepts())
            result = append(result,reduce(d));
        return result;
    }

    private R reduce(Department d) {
        R result = visit(d);
        result = append(result,reduce(d.getManager()));
        for (Department s : d.getSubdepts())
            result = append(result,reduce(s));
        for (Employee e : d.getEmployees())
            result = append(result,reduce(e));
        return result;
    }

    private R reduce(Employee e) {
        return visit(e);
    }

}