OnJava8-Examples/patterns/trash/Trash.java

//: patterns/trash/Trash.java
// Base class for Trash recycling examples.
package patterns.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(ArrayList bin) {
    Iterator e = bin.iterator();
    double val = 0.0f;
    while(e.hasNext()) {
      // One kind of RTTI:
      // A dynamically-checked cast
      Trash t = (Trash)e.next();
      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 ArrayList trashTypes = 
    new ArrayList();
  public static Trash factory(Info info) 
      throws PrototypeNotFoundException, 
      CannotCreateTrashException {
    for (Object trashType : trashTypes) {
      // Somehow determine the new type
      // to create, and create one:
      Class tc = (Class) trashType;
      if (tc.getName().contains(info.id)) {
        try {
          // Get the dynamic constructor method
          // 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[]{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.add(
        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;
    }
  }
} ///:~