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--;
        }
    }
    
    
}
 
public class TestTV {
    public static void main(String[] args) {
      TV tv1=new TV();
      tv1.turnOn();
     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);
      
      
  }

}
 

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public class circle {
     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;
        }
}
package kk;
 
public class Dmc {
      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());
             
        }
}

　　

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package kk;
 
public class Scircle {
     private double radius;
        public Scircle() {
            this.radius=1;
        }
        public Scircle(double radius){
            this.radius=radius;
        }
        public double getArea() {
            return Math.PI*radius*radius;
        }
        public double getPerimeter() {
            return 2*Math.PI*radius;
        }
        public static void main(String[] args) {
            Scircle cir1=new Scircle();
            System.out.println("The area of the circle of radius "+cir1.radius+" is "+cir1.getArea());
            Scircle cir2=new Scircle(10);
            System.out.println("The area of the circle of radius "+cir2.radius+" is "+cir2.getArea());
        }
}