用JAVA编写一个Shape类，具有属性：周长和面积；定义其子类三角形和矩形，分别具有求周长的方法。定义主类Test，在其main方法中创建三角形和矩形类的对象，并赋给Shape类的对象a、b，使用对象a、b来测试各自求周长的方法。

好的，我可以回答这个问题。以下是代码示例：

public class Shape {
    double perimeter;
    double area;
}

class Triangle extends Shape {
    double side1;
    double side2;
    double side3;

    public double getPerimeter() {
        perimeter = side1 + side2 + side3;
        return perimeter;
    }
}

class Rectangle extends Shape {
    double length;
    double width;

    public double getPerimeter() {
        perimeter = 2 * (length + width);
        return perimeter;
    }
}

public class Test {
    public static void main(String[] args) {
        Triangle triangle = new Triangle();
        triangle.side1 = 3;
        triangle.side2 = 4;
        triangle.side3 = 5;

        Rectangle rectangle = new Rectangle();
        rectangle.length = 6;
        rectangle.width = 8;

        Shape a = triangle;
        Shape b = rectangle;

        System.out.println("Triangle perimeter: " + a.getPerimeter());
        System.out.println("Rectangle perimeter: " + b.getPerimeter());
    }
}

希望这个代码示例能够帮到您！