<%! double area(double r) { return Math.PI*r*r; } double perimeter(double r) { } %>

As an AI language model, I do not have personal opinions or feelings, but "null" is a term used in computer programming to represent an empty or non-existent value. It is often used to indicate that a variable or data field has not been assigned a value or is uninitialized.

相关问题

用java 1定义接口IShape，该接口有2个方法，方法一（求周长）：double perimeter(),方法二（求面积）：double area();2自行定义圆类（Circle），实现IShape接口；3自行定义矩形类（Rectagle），实现IShape接口；然后进行测试

好的，以下是实现的Java代码：

interface IShape {
    double perimeter(); // 求周长
    double area();      // 求面积
}

class Circle implements IShape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double perimeter() {
        return 2 * Math.PI * radius;
    }

    @Override
    public double area() {
        return Math.PI * Math.pow(radius, 2);
    }
}

class Rectangle implements IShape {
    private double length;
    private double width;

    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }

    @Override
    public double perimeter() {
        return 2 * (length + width);
    }

    @Override
    public double area() {
        return length * width;
    }
}

public class Test {
    public static void main(String[] args) {
        Circle circle = new Circle(5);
        Rectangle rectangle = new Rectangle(3, 4);
        
        System.out.println("圆的周长：" + circle.perimeter());
        System.out.println("圆的面积：" + circle.area());
        System.out.println("矩形的周长：" + rectangle.perimeter());
        System.out.println("矩形的面积：" + rectangle.area());
    }
}

输出结果为：

圆的周长：31.41592653589793
圆的面积：78.53981633974483
矩形的周长：14.0
矩形的面积：12.0

编写Point、Circle、 Cylinder三个类之间具有层次结构的类。 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。 要求：所有的属性都是私有的。 提示：圆继承的点作为圆心，圆柱体继承 圆作为底面和顶面。 最终定义测试类。

class Point {
private double x;
private double y;

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

public double area() {
return 0;
}

@Override
public String toString() {
return "Point(" + x + ", " + y + ")";
}
}

class Circle extends Point {
private double radius;

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

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

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

@Override
public String toString() {
return "Circle(" + super.toString() + ", " + radius + ")";
}
}

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 area() {
return 2 * super.area() + 2 * Math.PI * radius * height;
}

public double volume() {
return super.area() * height;
}

@Override
public String toString() {
return "Cylinder(" + super.toString() + ", " + height + ")";
}
}

public class Test {
public static void main(String[] args) {
Point p = new Point(0, 0);
System.out.println(p + " Area: " + p.area());

Circle c = new Circle(0, 0, 5);
System.out.println(c + " Area: " + c.area() + " Perimeter: " + c.perimeter());

Cylinder cy = new Cylinder(0, 0, 5, 10);
System.out.println(cy + " Area: " + cy.area() + " Volume: " + cy.volume());
}
}