public class Polygon {

    public int sides;

    public double area;

    public int getNumberOfSides() {

        System.out.println(sides);

        return sides;

    }

/**重写toString*/

    @Override

    public String toString() {

        return "边数为：" + this.sides;

    }

/**构造方法*/

    public Polygon(int a) {

        this.sides = a;

        System.out.println("在Polygon的构造器中");

    }

}
Triangle 继承 Polygon

public class Triangle extends Polygon {

    public int base;

    public int height;

    public double area;

    /**

     * 构造方法

     *

     * @param base三角形底边

     * @param height三角形高

     */

    public Triangle(int base, int height) {

        super(3);

        this.base = base;

        this.height = height;

        System.out.println("在Triangle类的构造器中");

    }

    @Override

    /**

     * 重写String完成输出

     */

    public String toString() {

        return "三角形底：" + this.base + "     三角形高：" + this.height;

    }

    /**

     * 三角形面积计算

     *

     * @return三角形面积

     */

    public double getArea() {

        return (this.base) * (this.height) / 2;

    }

}

public class areaTest {

    public static void main(String[] args) {

        Polygon a = new Polygon(3);

        System.out.println(a.getNumberOfSides());// 添加方法输出

        System.out.println(a.toString());// 重写String

        Triangle b = new Triangle(4, 3);

        System.out.println(b.toString());

        System.out.println(b.getArea());

    }

}

public class Television {

    private int channel = 2;

    private int volume;

    /**

     * 频道

     * @param channel获取频道

     */

    public void SetChannel(int channel) {

        if (channel > 1000 || channel < 1) {

            return;

        } else {

            this.channel = channel;

        }

    }

    /** 频道访问器 */

    public int GetChannel() {

        return this.channel;

    }

    /**

     * 音量

     *

     * @param volume获取音量

     */

    public void SetVolume(int volume) {

        if (volume >= 0 && volume <= 10) {

            this.volume = volume;

        } else {

            return;

        }

    }

    /** 音量访问器 */

    public int GetVolume() {

        return this.volume;

    }

    /**

     * 构造器

     *

     * @param channel

     *            频道

     * @param volume

     *            音量

     */

    public Television(int channel, int volume) {

        this.SetChannel(channel);

        this.SetVolume(volume);

    }

    /**重写*/

    @Override

    public String toString()

    {

        return "频道："+GetChannel()+"\n音量："+GetVolume();

    }

}

public class WatchTelevision {

    public static void main(String[] args) {

        String c = JOptionPane.showInputDialog(null, "请输入频道");

        String v = JOptionPane.showInputDialog(null, "请输入音量");

        int channel = Integer.parseInt(c);

        int volume = Integer.parseInt(v);

        Television t = new Television(channel, volume);

        System.out.println(t);

    }

}