定义一个接口Shape，包含计算面积和计算周长的抽象方法；定义实现Shape的几种类，比如矩形、圆形、等边三角形 测试几种子类，求它们的面积和周长

以下是一个可能的实现，包括Shape接口和三个实现类Rectangle、Circle和EquilateralTriangle：

public interface Shape {
    double getArea();
    double getPerimeter();
}

public class Rectangle implements Shape {
    private double width;
    private double height;

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

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

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

public class Circle implements Shape {
    private double radius;

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

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

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

public class EquilateralTriangle implements Shape {
    private double side;

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

    public double getArea() {
        return Math.sqrt(3) / 4 * side * side;
    }

    public double getPerimeter() {
        return 3 * side;
    }
}

我们可以编写一个简单的测试程序来测试这些类：

public class ShapeTest {
    public static void main(String[] args) {
        Shape rectangle = new Rectangle(5, 3);
        Shape circle = new Circle(4);
        Shape equilateralTriangle = new EquilateralTriangle(6);

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

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

        System.out.println("Equilateral Triangle:");
        System.out.println("Area: " + equilateralTriangle.getArea());
        System.out.println("Perimeter: " + equilateralTriangle.getPerimeter());
    }
}

输出结果应该是：

Rectangle:
Area: 15.0
Perimeter: 16.0
Circle:
Area: 50.26548245743669
Perimeter: 25.132741228718345
Equilateral Triangle:
Area: 15.588457268119896
Perimeter: 18.0