哪个大佬救救孩子吧，想不出来怎么写

[qq_45351181]

（1）设计一个形状类 Shape，包含一个 getArea()方法，该方法不包含实际语句。 （2）在 Shape 类基础上设计圆形、矩形、三角形和梯形四个子类，要求根据实 际形状重写 getArea()方法。 （3）设计一个 TestShape 类，包含变量 area（存储总面积）、静态方法 countArea(Shapes)，该方法负责把参数中的形状面积加入到 area 中。在 main 方 法中新建（2）中四种类型的对象 shape1、shape2、shape3、shape4，通过调用 countArea 方法把四个对象面积累加到 area 中，最后输出 area。

这个TestShape类和主函数怎么写啊？

[winner245]

public class TestShape {
    public static void main(String[] args) {
        Shape shape1 = new Circle(10);
        Shape shape2 = new Rectangle(5,10); 
        Shape shape3 = new Triangle(1,2,3); // a, b, c
        Shape shape4 = new Trapezoid(3, 5, 4);  // a, b, h

        double area = countArea(shape1, shape2, shape3, shape4);
        System.out.println(area);
    }

    private static double countArea(Shape...shapes) {
        double area = 0.0;
        for (Shape shape : shapes)  area += shape.getArea();
        return area;
    }
}

abstract class Shape {
    public abstract double getArea();
}

class Circle extends Shape {
    private double radius;

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

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

class Rectangle extends 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;
    }
}

class Triangle extends Shape {
    private double a;
    private double b;
    private double c;

    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    @Override
    public double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p-a) * (p-b) * (p-c));
    }
}

class Trapezoid extends Shape {
    private double a;
    private double b;
    private double h;

    public Trapezoid(double a, double b, double h) {
        this.a = a;
        this.b = b;
        this.h = h;
    }

    @Override
    public double getArea() {
        return (a + b) * h / 2;
    }
}

[winner245]

for 的作用是循环，就是对每个shape都分别计算其面积，并累加

[qq_45351181]

引用 1 楼 winner245的回复:

public class TestShape {
    public static void main(String[] args) {
        Shape shape1 = new Circle(10);
        Shape shape2 = new Rectangle(5,10); 
        Shape shape3 = new Triangle(1,2,3); // a, b, c
        Shape shape4 = new Trapezoid(3, 5, 4);  // a, b, h

        double area = countArea(shape1, shape2, shape3, shape4);
        System.out.println(area);
    }

    private static double countArea(Shape...shapes) {
        double area = 0.0;
        for (Shape shape : shapes)  area += shape.getArea();
        return area;
    }
}

abstract class Shape {
    public abstract double getArea();
}

class Circle extends Shape {
    private double radius;

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

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

class Rectangle extends 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;
    }
}

class Triangle extends Shape {
    private double a;
    private double b;
    private double c;

    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    @Override
    public double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p-a) * (p-b) * (p-c));
    }
}

class Trapezoid extends Shape {
    private double a;
    private double b;
    private double h;

    public Trapezoid(double a, double b, double h) {
        this.a = a;
        this.b = b;
        this.h = h;
    }

    @Override
    public double getArea() {
        return (a + b) * h / 2;
    }
}

蟹蟹，能问下代码中for的作用吗？

[qq_45351181]

引用 1 楼 winner245的回复:

public class TestShape {
    public static void main(String[] args) {
        Shape shape1 = new Circle(10);
        Shape shape2 = new Rectangle(5,10); 
        Shape shape3 = new Triangle(1,2,3); // a, b, c
        Shape shape4 = new Trapezoid(3, 5, 4);  // a, b, h

        double area = countArea(shape1, shape2, shape3, shape4);
        System.out.println(area);
    }

    private static double countArea(Shape...shapes) {
        double area = 0.0;
        for (Shape shape : shapes)  area += shape.getArea();
        return area;
    }
}

abstract class Shape {
    public abstract double getArea();
}

class Circle extends Shape {
    private double radius;

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

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

class Rectangle extends 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;
    }
}

class Triangle extends Shape {
    private double a;
    private double b;
    private double c;

    public Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    @Override
    public double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p-a) * (p-b) * (p-c));
    }
}

class Trapezoid extends Shape {
    private double a;
    private double b;
    private double h;

    public Trapezoid(double a, double b, double h) {
        this.a = a;
        this.b = b;
        this.h = h;
    }

    @Override
    public double getArea() {
        return (a + b) * h / 2;
    }
}

蟹蟹，能问下代码中for的作用吗？