trash.java

Thinking_in_C___2.rar

//: C25:Trash.java
// From Thinking in C++, 2nd Edition
// at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Base class for Trash recycling examples
package c16.trash;
import java.util.*;
import java.lang.reflect.*;

public abstract class Trash {
  private double weight;
  Trash(double wt) { weight = wt; }
  Trash() {}
  public abstract double value();
  public double weight() { return weight; }
  // Sums the value of Trash in a bin:
  public static void sumValue(Vector bin) {
    Enumeration e = bin.elements();
    double val = 0.0f;
    while(e.hasMoreElements()) {
      // One kind of RTTI:
      // A dynamically-checked cast
      Trash t = (Trash)e.nextElement();
      val += t.weight() * t.value();
      System.out.println(
        "weight of " +
        // Using RTTI to get type
        // information about the class:
        t.getClass().getName() +
        " = " + t.weight());
    }
    System.out.println("Total value = " + val);
  }
  // Remainder of class provides support for
  // prototyping:
  public static class PrototypeNotFoundException
      extends Exception {}
  public static class CannotCreateTrashException
      extends Exception {}
  private static Vector trashTypes =
    new Vector();
  public static Trash factory(Info info)
      throws PrototypeNotFoundException,
      CannotCreateTrashException {
    for(int i = 0; i < trashTypes.size(); i++) {
      // Somehow determine the new type
      // to create, and create one:
      Class tc =
        (Class)trashTypes.elementAt(i);
      if (tc.getName().indexOf(info.id) != -1) {
        try {
          // Get the dynamic constructor member function
          // that takes a double argument:
          Constructor ctor =
            tc.getConstructor(
              new Class[] {double.class});
          // Call the constructor to create a
          // new object:
          return (Trash)ctor.newInstance(
            new Object[]{new Double(info.data)});
        } catch(Exception ex) {
          ex.prinTStackTrace();
          throw new CannotCreateTrashException();
        }
      }
    }
    // Class was not in the list. Try to load it,
    // but it must be in your class path!
    try {
      System.out.println("Loading " + info.id);
      trashTypes.addElement(
        Class.forName(info.id));
    } catch(Exception e) {
      e.prinTStackTrace();
      throw new PrototypeNotFoundException();
    }
    // Loaded successfully. Recursive call
    // should work this time:
    return factory(info);
  }
  public static class Info {
    public String id;
    public double data;
    public Info(String name, double data) {
      id = name;
      this.data = data;
    }
  }
} ///:~