第十四章 类型信息

.class和Class.forName()

        有时候需要获得Class对象的引用，可以通过类名.class或者Class.forName("类名")来获得。两者的区别是，使用.class来创建对Class对象的引用时，不会自动地初始化该Class对象，而Class.forName()会。

RTTI和反射机制

        RTTI：运行时类型信息(Run-Time Type Information)

        RTTI和反射之间的区别在于，对RTTI来说，编译器在编译时打开和检查.class文件，而对反射机制来讲，.class文件在编译时是不可获取的，所以是在运行时打开和检查.class文件。

工厂方法

1. 简单工厂

public abstract class Shape {

	private String name;

	public abstract void draw();

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Shape(String name) {
		super();
		this.name = name;
	}

}

public class Circle extends Shape {

	public Circle(String name) {
		super(name);
	}

	@Override
	public void draw() {
		System.out.printf("draw %s.\n", this.getName());
	}
	
}

public class Square extends Shape {

	public Square(String name) {
		super(name);
	}

	@Override
	public void draw() {
		System.out.printf("draw %s.\n", this.getName());
	}

}

public class SimpleFactory {

	public static Shape drawShape(String shapeType) {
		if (shapeType == null || "".equals(shapeType))
			return null;
		if ("circle".equalsIgnoreCase(shapeType)) {
			return new Circle(shapeType);
		} else if ("square".equalsIgnoreCase(shapeType)) {
			return new Square(shapeType);
		}
		return null;
	}

	// 测试方法
	public static void main(String[] args) {
		Shape circle = SimpleFactory.drawShape("circle");
		circle.draw();
		Shape square = SimpleFactory.drawShape("square");
		square.draw();
	}
}

2. 工厂方法

    增加一个ShapeFactory抽象类，CircleFactory和SquareFactory均继承自ShapeFactory，来实现获取Shape的功能，分离出简单工厂中的SimpleFactory的if else判断。

public abstract class ShapeFactory {

	public abstract Shape drawShape(String shapeType);
}

public class CircleFactory extends ShapeFactory {

	@Override
	public Shape drawShape(String shapeType) {
		return new Circle(shapeType);
	}

}

public class SquareFactory extends ShapeFactory {

	@Override
	public Shape drawShape(String shapeType) {
		return new Square(shapeType);
	}

}

public static void main(String[] args) {
	ShapeFactory abstractDraw = new CircleFactory();
	Shape circle = abstractDraw.drawShape("circle");
	circle.draw();
}

3. 抽象工厂

新增加和Shape同一级别的Color，添加一个AbstractFactory来获取Shape和Color，添加一个FactoryProducer来获取ShapeFactory或ColorFactory。

public abstract class Color {

	private String name;

	public abstract void fill();

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Color(String name) {
		super();
		this.name = name;
	}

}

public class Blue extends Color {

	public Blue(String name) {
		super(name);
	}

	@Override
	public void fill() {
		System.out.printf("fill %s color.\n", this.getName());
	}

}

public class Red extends Color {

	public Red(String name) {
		super(name);
	}

	@Override
	public void fill() {
		System.out.printf("fill %s color.\n", this.getName());
	}

}

public abstract class AbstractFactory {

	public abstract Color getColor(String color);

	public abstract Shape getShape(String shapeType);

}

public class ColorFactory extends AbstractFactory {

	@Override
	public Color getColor(String color) {
		if (color == null || "".equals(color))
			return null;
		if ("red".equalsIgnoreCase(color)) {
			return new Red(color);
		} else if ("blue".equalsIgnoreCase(color)) {
			return new Blue(color);
		}
		return null;
	}

	@Override
	public Shape getShape(String shapeType) {
		return null;
	}

}

public class ShapeFactory extends AbstractFactory {

	@Override
	public Color getColor(String color) {
		return null;
	}

	@Override
	public Shape getShape(String shapeType) {
		if (shapeType == null || "".equals(shapeType))
			return null;
		if ("circle".equalsIgnoreCase(shapeType)) {
			return new Circle(shapeType);
		} else if ("square".equalsIgnoreCase(shapeType)) {
			return new Square(shapeType);
		}
		return null;
	}

}

public class FactoryProducer {

	public static AbstractFactory getFactory(String choice) {
		if (choice == null || "".equals(choice))
			return null;
		if ("shape".equalsIgnoreCase(choice)) {
			return new ShapeFactory();
		} else if ("color".equalsIgnoreCase(choice)) {
			return new ColorFactory();
		}
		return null;
	}

	public static void main(String[] args) {
		AbstractFactory shapeFactory = FactoryProducer.getFactory("shape");
		Shape circle = shapeFactory.getShape("circle");
		circle.draw();
		AbstractFactory colorFactory = FactoryProducer.getFactory("color");
		Color red = colorFactory.getColor("red");
		red.fill();
	}
}