参照类图编写类代码； （2）定义图形抽象类，定义抽象draw方法，并为具体图形类定义具体方法的实 现； （3）设计并定义具体图形面积计算、周长计算方法； （4）编写Test类，测试draw方法

1. 类代码

abstract class Shape {
    public abstract void draw();
    public abstract double getArea();
    public abstract double getPerimeter();
}

class Circle extends Shape {
    private double radius;

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

    public void draw() {
        System.out.println("Drawing a circle");
    }

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

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

class Rectangle extends Shape {
    private double width;
    private double height;

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

    public void draw() {
        System.out.println("Drawing a rectangle");
    }

    public double getArea() {
        return width * height;
    }

    public double getPerimeter() {
        return 2 * (width + height);
    }
}

class Square extends Shape {
    private double side;

    public Square(double side) {
        this.side = side;
    }

    public void draw() {
        System.out.println("Drawing a square");
    }

    public double getArea() {
        return side * side;
    }

    public double getPerimeter() {
        return 4 * side;
    }
}

2. 图形抽象类和具体方法的实现

abstract class Shape {
    public abstract void draw();
    public abstract double getArea();
    public abstract double getPerimeter();
}

class Circle extends Shape {
    private double radius;

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

    public void draw() {
        System.out.println("Drawing a circle");
    }

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

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

class Rectangle extends Shape {
    private double width;
    private double height;

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

    public void draw() {
        System.out.println("Drawing a rectangle");
    }

    public double getArea() {
        return width * height;
    }

    public double getPerimeter() {
        return 2 * (width + height);
    }
}

class Square extends Shape {
    private double side;

    public Square(double side) {
        this.side = side;
    }

    public void draw() {
        System.out.println("Drawing a square");
    }

    public double getArea() {
        return side * side;
    }

    public double getPerimeter() {
        return 4 * side;
    }
}

3. 具体图形面积计算、周长计算方法

在上面的类中已经定义了具体图形面积计算、周长计算方法，分别是getArea()和getPerimeter()方法。

4. Test类

public class Test {
    public static void main(String[] args) {
        Shape circle = new Circle(5);
        Shape rectangle = new Rectangle(3, 4);
        Shape square = new Square(2);

        circle.draw();
        System.out.println("Area of circle: " + circle.getArea());
        System.out.println("Perimeter of circle: " + circle.getPerimeter());

        rectangle.draw();
        System.out.println("Area of rectangle: " + rectangle.getArea());
        System.out.println("Perimeter of rectangle: " + rectangle.getPerimeter());

        square.draw();
        System.out.println("Area of square: " + square.getArea());
        System.out.println("Perimeter of square: " + square.getPerimeter());
    }
}

输出结果：

Drawing a circle
Area of circle: 78.53981633974483
Perimeter of circle: 31.41592653589793
Drawing a rectangle
Area of rectangle: 12.0
Perimeter of rectangle: 14.0
Drawing a square
Area of square: 4.0
Perimeter of square: 8.0