Think in Java(五)：多态

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public class Shapes {
	private static RandomShapeGenerator gen = new RandomShapeGenerator();

	public static void main(String[] args) {
		Shape[] shapeArr = new Shape[9]; 
		// 填充数组
		for (int i = 0; i < shapeArr.length; i++){
			shapeArr[i] = gen.next();
		}
		// 动态调用方法
		for (Shape shape : shapeArr){ 
			shape.draw(); 
		}
	}
}

class RandomShapeGenerator {
	private Random rand = new Random(47);

	public Shape next() {
		switch (rand.nextInt(3)) {
			default:
			case 0:
				return new Circle();
			case 1:
				return new Square();
			case 2:
				return new Triangle();
			}
	}
}

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

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

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

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

class Triangle extends Shape {
	public void draw() {
		System.out.println("Triangle.draw()");
	}

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

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

	public void erase() {
		System.out.println("Square.erase()");
	}
}
/* Output:
Triangle.draw()
Triangle.draw()
Square.draw()
Triangle.draw()
Square.draw()
Triangle.draw()
Square.draw()
Triangle.draw()
Circle.draw()
*///:~

public class PrivateOverride {
	private void f() {
		print("private f()");
	}

	public static void main(String[] args) {
		PrivateOverride po = new Derived();
		po.f();
	}
}

class Derived extends PrivateOverride {
	public void f() {
		print("public f()");
	}
} 
/* Output:
private f()
*///:~

class Meal {
	Meal() {
		print("Meal()");
	}
}

class Bread {
	Bread() {
		print("Bread()");
	}
}

class Cheese {
	Cheese() {
		print("Cheese()");
	}
}

class Lettuce {
	Lettuce() {
		print("Lettuce()");
	}
}

class Lunch extends Meal {
	Lunch() {
		print("Lunch()");
	}
}

class PortableLunch extends Lunch {
	PortableLunch() {
		print("PortableLunch()");
	}
}

public class Sandwich extends PortableLunch {
	private Bread bread = new Bread();

	private Cheese cheese = new Cheese();

	private Lettuce lettuce = new Lettuce();

	public Sandwich() {
		print("Sandwich()");
	}

	public static void main(String[] args) {
		new Sandwich();
	}
} 
/* Output:
Meal()
Lunch()
PortableLunch()
Bread()
Cheese()
Lettuce()
Sandwich()

class Glyph {
	void draw() {
		print("Glyph.draw()");
	}

	Glyph() {
		print("Glyph() before draw()");
		this.draw();
		print("Glyph() after draw()");
	}
}

class RoundGlyph extends Glyph {
	private int radius = 1;

	RoundGlyph(int r) {
		radius = r;
		print("RoundGlyph.RoundGlyph(), radius = " + radius);
	}

	void draw() {
		print("RoundGlyph.draw(), radius = " + radius);
	}
}

public class PolyConstructors {
	public static void main(String[] args) {
		new RoundGlyph(5);
	}
} 
/* Output:
Glyph() before draw()
RoundGlyph.draw(), radius = 0
Glyph() after draw()
RoundGlyph.RoundGlyph(), radius = 5
*///:~

之所以调用的是子类的draw方法，this的含义是谁调用我，this指向的就是谁，Glyph构造器是通过RoundGlyph类构造器中super()方法触发，所以this指向的是RoundGlyph中的draw方法

Think in Java(五)：多态

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原文地址：http://blog.csdn.net/zdp072/article/details/43058439