有一类实体是形状（Shape）包含矩形（Rectangle）、圆形（Circle）等，请使用工厂方法模式（FactoryMethod）实现该要求。 1.画出类结构图 2.采用java语言实现该工厂方法模式，并写测试程序main（）进行测试

以下是类结构图：

                                      +------ ShapeFactory ------+
                                      |                           |
                                      |                           |
                                      |  createShape(shapeType)   |
                                      |                           |
                                      +---------------+-----------+
                                                      |
                                                      |
                ------------------------------------------------------
                |                          |                          |
                |                          |                          |
+-------- Rectangle -------+   +------- Circle --------+   +------- Triangle --------+
|                          |   |                        |   |                            |
|  -length: double         |   |  -radius: double        |   |  -base: double             |
|  -width: double          |   |                        |   |  -height: double           |
|                          |   |                        |   |                            |
|  +Rectangle(length,      |   |  +Circle(radius)        |   |  +Triangle(base, height)   |
|             width)       |   |                        |   |                            |
|  +getArea(): double      |   |  +getArea(): double     |   |  +getArea(): double        |
|                          |   |                        |   |                            |
+--------------------------   +------------------------   +----------------------------+

以下是使用 Java 实现的代码：

// Shape.java
public interface Shape {
    double getArea();
}

// Rectangle.java
public class Rectangle implements Shape {
    private double length;
    private double width;

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

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

// Circle.java
public class Circle implements Shape {
    private double radius;

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

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

// Triangle.java
public class Triangle implements Shape {
    private double base;
    private double height;

    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }

    @Override
    public double getArea() {
        return 0.5 * base * height;
    }
}

// ShapeFactory.java
public class ShapeFactory {
    public Shape createShape(String shapeType) {
        if (shapeType.equals("Rectangle")) {
            return new Rectangle(5.0, 3.0);
        } else if (shapeType.equals("Circle")) {
            return new Circle(4.0);
        } else if (shapeType.equals("Triangle")) {
            return new Triangle(5.0, 3.0);
        } else {
            return null;
        }
    }
}

// Main.java
public class Main {
    public static void main(String[] args) {
        ShapeFactory shapeFactory = new ShapeFactory();

        Shape rectangle = shapeFactory.createShape("Rectangle");
        System.out.println("Rectangle area: " + rectangle.getArea());

        Shape circle = shapeFactory.createShape("Circle");
        System.out.println("Circle area: " + circle.getArea());

        Shape triangle = shapeFactory.createShape("Triangle");
        System.out.println("Triangle area: " + triangle.getArea());
    }
}

运行 `Main.java` 后，输出如下：

Rectangle area: 15.0
Circle area: 50.26548245743669
Triangle area: 7.5