Point类中有xy属性，定义构造函数，及计算面积的方法double area0和toString0方 法； Circle类中增加一个半径double radius属性，定义构造函数，及计算面积的方法double area0(重写父类的方法)、计算周长的方法double perimeterQ和toString0方法； Cylinder类增加一个高height属性，定义构 造函数，及计算表面积的方法double area0( 重写父类的方法)和计算体积的方法double volume0和toString方法。

Point类：

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

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

public double area0() {
return 0.0;
}

public String toString0() {
return "(" + this.x + ", " + this.y + ")";
}
}

Circle类：

public class Circle extends Point {
private double radius;

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

@Override
public double area0() {
return Math.PI * this.radius * this.radius;
}

public double perimeterQ() {
return 2 * Math.PI * this.radius;
}

@Override
public String toString0() {
return "Circle: center" + super.toString0() + ", radius=" + this.radius;
}
}

Cylinder类：

public class Cylinder extends Circle {
private double height;

public Cylinder(double x, double y, double radius, double height) {
super(x, y, radius);
this.height = height;
}

@Override
public double area0() {
return 2 * Math.PI * this.radius * (this.radius + this.height);
}

public double volume0() {
return Math.PI * this.radius * this.radius * this.height;
}

@Override
public String toString0() {
return "Cylinder: center" + super.toString0() + ", radius=" + this.radius + ", height=" + this.height;
}
}