Multi.java (Multimethods in Java)

Multi.java

package util;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * This class implements multiple dispatch (aka multimethods) using reflection.
 * The idea is to choose the method based not only on the runtime type of the
 * receiver, but also on the runtime type of the arguments. Normally Java
 * selects amongst overloaded alternatives using the static type.
 *
 * The current version doesn't implement true multiple dispatch, as the system
 * only searches for methods with the exact runtime parameters. See the
 * dispatch() method for more details. The rationale is that I currently don't
 * need more than that.
 */
public class Multi
{
  /*****************************************************************************
   * Tries to find a method of obj with the given name and whose parameter types
   * are the types of the object in params. Beware that the search only
   * considers the exact runtime type of the objects. e.g. a method taking an
   * Object parameter won't be found when searching for a similarly named method
   * taking a String parameter.
   *
   * To know which exceptions are thrown and when they arise, see the linked
   * methods.
   *
   * @see Class#getMethod()
   * @see Method#invoke()
   */
  public static Object dispatch(Object receiver, String name, Object... params)
    throws NoSuchMethodException, SecurityException, IllegalAccessException,
      IllegalArgumentException, InvocationTargetException
  {
    Class<?>[] classes = new Class[params.length];

    int i = 0;
    for (Object o : params) {
      classes[i] = o.getClass();
    }

    Method method = receiver.getClass().getMethod(name, classes);
    return method.invoke(receiver, params);
  }

  /*****************************************************************************
   * Optimized version of the dispatch() method, for methods of one argument.
   */
  public static Object dispatch1(Object receiver, String name, Object param)
    throws NoSuchMethodException, SecurityException, IllegalAccessException,
      IllegalArgumentException, InvocationTargetException
  {
    Method method = receiver.getClass().getMethod(name, param.getClass());
    return method.invoke(receiver, param);
  }

  /*****************************************************************************
   * A chill pill around dispatch(), turning all the check exceptions into a
   * runtime exception. For when it should always work.
   * @throws Throwable
   *
   * @see Multi#dispatch()
   */
  public static Object dynDispatch(Object receiver, String name, Object... params)
  {
    try {
      return dispatch(receiver, name, params);
    }
    catch (NoSuchMethodException | SecurityException | IllegalAccessException
      | IllegalArgumentException e)
    {
      e.printStackTrace();
      throw new RuntimeException("Illegal multimethod call.");
    }
    catch (InvocationTargetException e)
    {
      throw new RuntimeException(e.getCause());
    }
  }
}