A simple static factory method. : Factory Pattern « Design Pattern « Java Tutorial

1. Java Tutorial
2. Design Pattern
3. Factory Pattern

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

abstract class Shape {
  public abstract void draw();

  public abstract void erase();

  public static Shape factory(String type) {
    if (type.equals("Circle"))
      return new Circle();
    if (type.equals("Square"))
      return new Square();
    throw new RuntimeException("Bad shape creation: " + type);
  }
}

class Circle extends Shape {
  Circle() {
  } // Package-access constructor

  public void draw() {
    System.out.println("Circle.draw");
  }

  public void erase() {
    System.out.println("Circle.erase");
  }
}

class Square extends Shape {
  Square() {
  } // Package-access constructor

  public void draw() {
    System.out.println("Square.draw");
  }

  public void erase() {
    System.out.println("Square.erase");
  }
}

public class ShapeFactory {
  public static void main(String args[]) {
    List<Shape> shapes = new ArrayList<Shape>();
    Iterator it = Arrays.asList(
        new String[] { "Circle", "Square", "Square", "Circle", "Circle", "Square" }).iterator();
    while (it.hasNext())
      shapes.add(Shape.factory((String) it.next()));

    it = shapes.iterator();
    
    while (it.hasNext()) {
      Shape s = (Shape) it.next();
      s.draw();
      s.erase();
    }
  }
}