JavaSE 第二十一讲 多态详解续2 10.8

1.抽象类

public abstract class AbstarctTest
{

}

2.抽象方法

public class Test
{
    public static void main(String[] args)
    {
    
    }
}

abstract class T
{
    public abstract void method();//抽象方法，有声明无实现

    public void test()//抽象类中可包含具体方法
    {
        System.out.println("test");
    }
}

class R extends T  //继承父类（抽象类）所有的抽象方法；否则，子类也要声明成一个abstract class
{
    public void method()
    {
        System.out.println("method");
    }
}

3.抽象类作用

public class Test2
{
    public static void main(String[] args)
    {
        Shape shape = new Triangle(10,6);

        int area = shape.computeArea();

        System.out.println("triangle:" + area);

        shape = new Rectangle(10,10);

        area = shape.computeArea();

        System.out.println("rectangle:" + area);
    }
}

abstract class Shape
{
    public abstract int computeArea();//计算形状面积
}

class Triangle extends Shape
{
    int width;
    int height;

    public Triangle(int width, int height)
    {
        this.width = width;
        this.height = height;
    }

    public int computeArea()
    {
        return (width * height) / 2;
    }
    
}

class Rectangle extends Shape
{
    int width;
    int height;

    public Rectangle(int width, int height)
    {
        this.width = width;
        this.height = height;       
    }

    public int computeArea()
    {
        return width * height;
    }
}