用java编写一个抽象类表示形状,其中有一个求面积的抽象方法。继承该抽象类分别编写三角形、园,矩形类,创建一个数组存放创建的各类图形对象,输出图形面积。

抽象类Shape：

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

三角形类Triangle：

public class Triangle extends Shape {
    private double base;
    private double height;
    
    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }
    
    public double getBase() {
        return base;
    }
    
    public double getHeight() {
        return height;
    }
    
    @Override
    public double getArea() {
        return 0.5 * base * height;
    }
}

圆类Circle：

public class Circle extends Shape {
    private double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    public double getRadius() {
        return radius;
    }
    
    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

矩形类Rectangle：

public class Rectangle extends Shape {
    private double width;
    private double height;
    
    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    
    public double getWidth() {
        return width;
    }
    
    public double getHeight() {
        return height;
    }
    
    @Override
    public double getArea() {
        return width * height;
    }
}

测试代码：

public class Test {
    public static void main(String[] args) {
        Shape[] shapes = new Shape[3];
        shapes[0] = new Triangle(3, 4);
        shapes[1] = new Circle(5);
        shapes[2] = new Rectangle(6, 7);
        
        for (Shape shape : shapes) {
            System.out.println("面积为：" + shape.getArea());
        }
    }
}

输出结果：

面积为：6.0
面积为：78.53981633974483
面积为：42.0