package haha_111;

public class Point {
    protected double x;
    protected double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public Point() {
        x = y = 0;
    }

    public double getX() {
        return x;
    }

    public void setX(double x) {
        this.x = x;
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }
}


public class Circle extends Point {
    protected double r;

    public Circle(double x, double y, double r) {
        super(x, y);
        this.r = r;
    }

    public Circle() {
        super();
        r = 0;
    }

    public double area() {
        return Math.PI * r * r;
    }

    public double getR() {
        return r;
    }

    public void setR(double r) {
        this.r = r;
    }
}


public class Cylinder extends Circle {
    protected double h;

    public Cylinder(double x, double y, double r, double h) {
        super(x, y, r);
        this.h = h;
    }

    public Cylinder() {
        super();
        h = 0;
    }

    public double volume() {
        return area() * h;
    }

    public double getH() {
        return h;
    }

    public void setH(double h) {
        this.h = h;
    }
}


public static void main(String[] args) {
    Cylinder c1 = new Cylinder();
    Cylinder c2 = new Cylinder(1, 2, 3, 4);
    System.out.println("c1(" + c1.getX() + "," + c1.getY() + "):r=" +
                       c1.getR() + ",h=" + c1.getH() + ",volume=" +
                       c1.volume());
    System.out.println("c2(" + c2.getX() + "," + c2.getY() + "):r=" +
                       c2.getR() + ",h=" + c2.getH() + ",volume=" +
                       c2.volume());

}

一般初学者在继承和多态时候都会遇见这个题目的，程序运行报错

错误信息："Point.java": 'class' or 'interface' expected at line 88, column 15


请高手指点！  谢谢！

[[it] 本帖最后由 hanzhu3366 于 2008-5-21 00:41 编辑 [/it]]

为什么有那么多public class啊？

只有继承没有多态。。没有同名函数
class Point {
    protected double x;
    protected double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public Point() {
        x = y = 0;
    }

    public double getX() {
        return x;
    }

    public void setX(double x) {
        this.x = x;
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }
}


 class Circle extends Point {
    protected double r;

    public Circle(double x, double y, double r) {
        super(x, y);
        this.r = r;
    }

    public Circle() {
        super();
        r = 0;
    }

    public double area() {
        return Math.PI * r * r;
    }

    public double getR() {
        return r;
    }

    public void setR(double r) {
        this.r = r;
    }
}


 class Cylinder extends Circle {
    protected double h;

    public Cylinder(double x, double y, double r, double h) {
        super(x, y, r);
        this.h = h;
    }

    public Cylinder() {
        super();
        h = 0;
    }

    public double volume() {
        return area() * h;
    }

    public double getH() {
        return h;
    }

    public void setH(double h) {
        this.h = h;
    }
}

class demo{

public static void main(String[] args) {
    Cylinder c1 = new Cylinder();
    Cylinder c2 = new Cylinder(1, 2, 3, 4);
    System.out.println("c1(" + c1.getX() + "," + c1.getY() + "):r=" +
                       c1.getR() + ",h=" + c1.getH() + ",volume=" +
                       c1.volume());
    System.out.println("c2(" + c2.getX() + "," + c2.getY() + "):r=" +
                       c2.getR() + ",h=" + c2.getH() + ",volume=" +
                       c2.volume());

}
}

难受中ing...
你不是帮别人写作业吧？这个貌似是群里提的问题...

这是一道作业题目！ 但我对类的封装和多态了解不够透彻~~

子类父类同名方法的应用。。因为java不像c++，都是引用。。当把子类对象赋给父类引用的时候都是子类覆盖父类方法。。抽象类是在一般基础上的扩展，它只能声明引用不能实例，但是由于是单继承概念的限制，所以提供接口。。

谢谢，我们现在只开了java，如果带着看c++，两门语言一起学，效率是不是强一些啊！？

效果肯定不好，等java入门后，稍微精通了，再去了解C++吧！不过等你精通java了，估计你是不会去看C++的！

貌似你还没有和hanzhu3366加为好友啊，或者他没有加你？
我已经把你们俩都“收编”啦，两位也在私底下“活动活动”啊！
呵呵， ！
希望和二位结盟！

java.lang.NoSuchMethodError: main
Exception in thread "main"

编译通过，运行报错！  在网上查的几种可能；
1、文件名定义有问题
2、没有主函数
3、环境变量设置问题！

......

呵呵，刚刚找出来了，文件名定义有点问题！

[[it] 本帖最后由 hanzhu3366 于 2008-5-22 00:59 编辑 [/it]]