JAVA语言程序设计课后习题----第七单元解析（仅供参考）

1　　本题水题，就是想让你理解继承的含义

 public class Animaal {
     public double weight;
     public void eat(){
     }
 }

 public class Bird extends Animaal {
     public int numberOfFins;
     public void fly(){}

 }

 public class Dog extends Animaal {
     public int numberOflegs;
     public void walk(){}

 }

 public class Fish extends Animaal{
     public int numberOfFins;
     public void swim(){}

 }

2　　本题主要考类的继承和方法的重写，方法的重写关键字@Override

 public class Circle {
     public int radius;
     public double getArea(){
         return Math.PI*radius*radius;
     }
 }

 public class Cylinder extends Circle {
     public double height;

     public Cylinder() {
     }

     public Cylinder(double height) {
         this.height = height;
     }
     public Cylinder(int radius,double height){
         this.radius=radius;
         this.height=height;
     }
     //    体积
     public double getVolume(){
         return Math.PI*radius*radius*height;
     }
     //    覆盖Circle 里面的getArea函数求圆柱的体积
     @Override
     public double getArea(){
         return Math.PI*radius*radius*2+2*Math.PI*radius*height;
     }
 }

 import java.util.Scanner;

 public class ch08 {
     public static void main(String[] args) {

         Scanner input = new Scanner(System.in);
         System.out.println("请输入圆柱的半径、高");
         Cylinder cylinder = new Cylinder(input.nextInt(),input.nextDouble());
         System.out.println("圆柱的体积为:"+cylinder.getVolume());
         System.out.println("圆柱的面积为:"+cylinder.getArea());
     }
 }

3　　本题水题，考的方法和上面两题类似，注意题目要求即可

 public class Auto {
     public double speed;
     //    启动的方法
     public void start(){
         System.out.println("插上钥匙、系上安全带、一脚把离合踩到底、挂上一档、打左转向、缓慢抬脚、汽车平稳启动");
     }
     //    加速的方法
     public void speedUp(){
         System.out.println("脚慢踩油门、松开油门、踩离合到底、换挡、加速完成");
     }
     //    停止的方法
     public void stop(){
         System.out.println("慢踩刹车、达到额定速度、松开刹车、踩离合、换挡、持续到速度为0");
     }
 }

 public class Bus extends Auto {
     public int passenger;
     public Bus(int passenger){this.passenger=passenger;}
     //    上车
     public int gotOn(){ return ++passenger;
     }
     //    下车
     public int gotOff(){return --passenger;}
 }

 import java.util.Scanner;

 public class ch09 {
     public static void main(String[] args) {
         Scanner input = new Scanner(System.in);
         System.out.println("请输入开始车上的人数");
         Bus bus = new Bus(input.nextInt());
         System.out.println("旅客上车");
         System.out.println(bus.gotOn());
         bus.start();
         bus.speedUp();
         System.out.println("旅客上下车");
         System.out.println(bus.gotOff());
         bus.stop();
     }
 }

4　　本题主要考继承和抽象方法，关键字@Override

　

 public class Shape {
     public int radius;
     public int l;
     public double getPrimeter(){
         return 0;
     }
     public double getArea(){return 0;}
 }

 public class Square extends Shape {
     public Square() {
     }

     public Square(int radius){this.radius=radius;}
     @Override
     public double getPrimeter(){
         return 4*radius;
     }
     @Override
     public double getArea(){
         return radius*radius;
     }

 }

 public class ch10 {
     public static void main(String[] args) {
         Square square = new Square(10);
         System.out.println("正方形的周长为:"+square.getPrimeter());
         System.out.println("正方形的面积为:"+square.getArea());
     }
 }

5　　本题主要考方法的覆盖，构造方法的重写

 public class Rectangle {
     public double length,width;

     public Rectangle(double length, double width) {
         this.length=length;
         this.width=width;
     }
 }

 public class Cuboid extends Rectangle{
     public double height;

     public Cuboid(double length, double width, double height) {
         super(length, width);
         this.height = height;
     }

     public double volume(){
         return length*width*height;
     }
 }

 public class ch11 {
     public static void main(String[] args) {
         System.out.println("长方体的长、宽、高分别为10、5、2!");
         Cuboid cuboid = new Cuboid(10,5,2);
         System.out.println("长方体的体积为:"+cuboid.volume());
     }
 }