carfield.com.hk: ShapeFactory2.java

Wed Dec 26 16:00:00 GMT 2001

ShapeFactory2

//: c05:shapefact2:ShapeFactory2.java
// Polymorphic factory methods.
package c05.shapefact2;
import java.util.*;
import com.bruceeckel.test.*;

interface Shape {
  void draw();
  void erase();
}

abstract class ShapeFactory {
  protected abstract Shape create();
  private static Map factories = new HashMap();
  public static void 
  addFactory(String id, ShapeFactory f) {
    factories.put(id, f);
  }
  // A Template Method:
  public static final 
  Shape createShape(String id) {
    if(!factories.containsKey(id)) {
      try {
        // Load dynamically
        Class.forName("c05.shapefact2." + id);
      } catch(ClassNotFoundException e) {
        throw new RuntimeException(
          "Bad shape creation: " + id);
      }
      // See if it was put in:
      if(!factories.containsKey(id))
        throw new RuntimeException(
          "Bad shape creation: " + id);
    }
    return 
      ((ShapeFactory)factories.get(id)).create();
  }
}

class Circle implements Shape {
  private Circle() {}
  public void draw() { 
    System.out.println("Circle.draw"); 
  }
  public void erase() { 
    System.out.println("Circle.erase");
  }
  private static class Factory 
  extends ShapeFactory {
    protected Shape create() { 
      return new Circle(); 
    }
  }
  static {
    ShapeFactory.addFactory(
      "Circle", new Factory());
  }
}

class Square implements Shape {
  private Square() {} 
  public void draw() { 
    System.out.println("Square.draw"); 
  }
  public void erase() { 
    System.out.println("Square.erase"); 
  }
  private static class Factory 
  extends ShapeFactory {
    protected Shape create() { 
      return new Square(); 
    }
  }
  static {
    ShapeFactory.addFactory(
      "Square", new Factory());
  }
}

public class ShapeFactory2 extends UnitTest {
  String shlist[] = { "Circle", "Square", 
    "Square", "Circle", "Circle", "Square" };
  List shapes = new ArrayList();
  public void test() {
    // This just makes sure it will complete 
    // without throwing an exception.
    for(int i = 0; i < shlist.length; i++)
      shapes.add(
        ShapeFactory.createShape(shlist[i]));
    Iterator i = shapes.iterator();
    while(i.hasNext()) {
      Shape s = (Shape)i.next();
      s.draw();
      s.erase();
    }
  }
  public static void main(String args[]) {
    new ShapeFactory2().test();
  }
} ///:~

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