Java 作业3

包含两张图片和填空题

4-1
abstract class Animal {
    void cry() {

    }

    String getName() {
        return null;
    }
}
class Dog extends Animal {
    private String name;
    Dog(String name) {
        this.name = name;
    }
    @Override
    public void cry() {
        System.out.println("汪汪");
    }
    @Override
    public String  getName() {
        return "我的名字叫"+name;
    }
}
public class SimulateTest
{
    public static void main(String[] args) {
        Animal dog = new Dog(" Bob ");
                System.out.println(dog.getName());
                dog.cry();
    }

}
4-2
import java.awt.*;

//
public class Main
{

    public static void main(String args[])
    {
        Shape ss[] =new Shape[4] ;

        ss[0] = new Rect(10,10);
        ss[1] = new Rect(8, 12);
        ss[2] = new Circle(5);
        ss[3] = new Circle(6);

        for(int i = 0; i < ss.length; i++)
        {
            System.out.println(ss[i].getArea());
        }

    }

}

abstract class Shape
{
    abstract int getArea();
}

class Rect extends Shape
{
    int     width;
    int     height;

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

    int getArea()
    {
        return width * height;
    }
}

class Circle extends Shape
{
    int radius;

    Circle(int radius)
    {
        this.radius=radius;
    }

    int getArea()
    {
        return (int)(radius*radius*3.1415926);
    }
}
4-3

abstract class Flyable {
    void fly() {

    }
}
abstract class Duck extends Flyable {
    public void quack() {
        System.out.println("我会呱呱呱");
    }
    public void swim() {
        System.out.println("我会游泳");
    }
    public abstract void display();

    @Override
    public void fly() {
        System.out.println("我会飞");
    }
}
class RedheadDuck extends Duck {
    public void display() {
        System.out.println("我是一只红头鸭");
    }
}

public class Main {
    public static void main(String[] args) {
        Duck rduck = new RedheadDuck();
        rduck.display();
        rduck.quack();
        rduck.swim();
        rduck.fly();
    }
}
4-4
Foo
Foo.Bar
4-5
test run
Test$1
4-6
Shape.draw()1
4-7
抽象方法
抽象类
4-8
sealed