作业1：

例题9.1 制作圆类，根据圆的半径求出周长及面积

package com.swift;//抽象的方法构成类，把属性和方法进行封装public class Circle {    // 两个方面一个是字段也称属性，另一个是方法，也称实现的功能    private double radius;    // 构造方法,有参构造    public Circle(double radius) {        this.radius = radius;    }    //方法的重载，参数不同    // 构造方法，无参构造    public Circle() {        this.radius = 1;    }    // 求圆面积的方法    public double getArea() {        return radius * radius * Math.PI;    }    // 求圆周长的方法    public double getPerimeter() {        return 2 * Math.PI * radius;    }    public void setRadius(double newRadius) {        this.radius=newRadius;    }}

圆类的展示类

package com.swift;public class DemoCircle {    public static void main(String[] args) {        Circle circle1=new Circle();        double area=circle1.getArea();        System.out.println(area);        Circle circle2=new Circle(10);        System.out.println(circle2.getArea());        System.out.println(circle1.getPerimeter());        System.out.println(circle2.getPerimeter());        double ridius=10;        double areaCircle=Math.PI*ridius*ridius;        System.out.println(areaCircle);        circle2.setRadius(5);        System.out.println(circle2.getArea());    }}

作业2：

把上边的两个圆的类合并成一个类，并实现同样功能

package com.swift;public class SimpleCircle {    private double radius;    public SimpleCircle() {        this.radius=1;    }    public SimpleCircle(double radius){        this.radius=radius;    }    public double getArea() {        // TODO Auto-generated method stub        return Math.PI*radius*radius;    }    public double getPerimeter() {        return 2*Math.PI*radius;    }        public static void main(String[] args) {        SimpleCircle cir1=new SimpleCircle();        System.out.println("The area of the circle of radius "+cir1.radius+" is "+cir1.getArea());        SimpleCircle cir2=new SimpleCircle(10);        System.out.println("The area of the circle of radius "+cir2.radius+" is "+cir2.getArea());    }}

作业3：

例题9.3 造一台电视机，并且实现调频道和调声音大小功能

package com.swift;public class TV {    public int channel=1;    public int volumeLevel=1;    public boolean on=false;        public TV() {            }    public void turnOn() {        on =true;        System.out.println("电视机已经打开了。");    }    public void turnOff() {        on=false;        System.out.println("电视机已经关闭了。");    }    public int getChannel() {        return channel;    }    public void setChannel(int channel) {        if(on) {            System.out.println("电视机已开，可以开始调台了。");            if(channel>=1&&channel<=120) {                this.channel = channel;                System.out.println("频道已经调到 "+channel+" 台");            }else {                System.out.println("你要调的频道不存在。");            }        }else {            System.out.println("电视机关着的时候是不能调台的");        }    }    public int getVolumeLevel() {        return volumeLevel;    }    public void setVolumeLevel(int volumeLevel) {        if(on) {            System.out.println("电视机已开，声音大小可调了");            if(volumeLevel>=1&&volumeLevel<=7) {                this.volumeLevel = volumeLevel;                System.out.println("声音的大小设置成了 "+volumeLevel+" 大小");            }        }else {            System.out.println("电视机关着的时候是不能调声音的");        }            }    public void channelUp() {        if(on&&channel<120) {            channel++;        }    }    public void channelDown() {        if(on&&channel>1) {            channel--;        }    }    public void volumeUp() {        if(on&&volumeLevel<7) {            volumeLevel++;        }    }    public void volumeDown() {        if(on&&volumeLevel>1) {            volumeLevel--;        }    }        }

测试电视机的类

package com.swift;public class TestTV {    public static void main(String[] args) {//        TV tv1=new TV();//        tv1.turnOff();//        tv1.setChannel(30);//        tv1.setVolumeLevel(3);                TV tv2=new TV();        tv2.turnOn();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.channelUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.channelUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.channelUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.volumeUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.volumeUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);        tv2.volumeUp();        System.out.println("TV2's channel is "+tv2.channel+" and volume is "+tv2.volumeLevel);                    }}