java/w4/Shape.java

package com.example.shape;

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

class Circle extends Shape {
    private double radius;
    private static final double PI = 3.1415926;
    
    public Circle(double radius) {
        if (radius <= 0) {
            throw new IllegalArgumentException("半径必须大于0");
        }
        this.radius = radius;
    }
    
    @Override
    public double getArea() {
        return PI * radius * radius;
    }
    
    public double getRadius() {
        return radius;
    }
    
    public void setRadius(double radius) {
        if (radius <= 0) {
            throw new IllegalArgumentException("半径必须大于0");
        }
        this.radius = radius;
    }
}

class Rectangle extends Shape {
    private double length;
    private double width;
    
    public Rectangle(double length, double width) {
        if (length <= 0 || width <= 0) {
            throw new IllegalArgumentException("长和宽必须大于0");
        }
        this.length = length;
        this.width = width;
    }
    
    @Override
    public double getArea() {
        return length * width;
    }
    
    public double getLength() {
        return length;
    }
    
    public void setLength(double length) {
        if (length <= 0) {
            throw new IllegalArgumentException("长必须大于0");
        }
        this.length = length;
    }
    
    public double getWidth() {
        return width;
    }
    
    public void setWidth(double width) {
        if (width <= 0) {
            throw new IllegalArgumentException("宽必须大于0");
        }
        this.width = width;
    }
}

class Triangle extends Shape {
    private double a;
    private double b;
    private double c;
    
    public Triangle(double a, double b, double c) {
        // 校验三边>0，且满足三角形三边关系（任意两边之和>第三边）
        if (a <= 0 || b <= 0 || c <= 0) {
            throw new IllegalArgumentException("边长必须大于0");
        }
        if (a + b <= c || a + c <= b || b + c <= a) {
            throw new IllegalArgumentException("不满足三角形三边关系，无法构成三角形");
        }
        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));
    }
    
    public double getA() {
        return a;
    }
    
    public void setA(double a) {
        if (a <= 0) {
            throw new IllegalArgumentException("边长必须大于0");
        }
        this.a = a;
        if (a + b <= c || a + c <= b || b + c <= a) {
            throw new IllegalArgumentException("不满足三角形三边关系，无法构成三角形");
        }
    }
    
    public double getB() {
        return b;
    }
    
    public void setB(double b) {
        if (b <= 0) {
            throw new IllegalArgumentException("边长必须大于0");
        }
        this.b = b;
        if (a + b <= c || a + c <= b || b + c <= a) {
            throw new IllegalArgumentException("不满足三角形三边关系，无法构成三角形");
        }
    }
    
    public double getC() {
        return c;
    }
    
    public void setC(double c) {
        if (c <= 0) {
            throw new IllegalArgumentException("边长必须大于0");
        }
        this.c = c;
        if (a + b <= c || a + c <= b || b + c <= a) {
            throw new IllegalArgumentException("不满足三角形三边关系，无法构成三角形");
        }
    }
}

class ShapeUtil {
    public static void printArea(Shape shape) {
        if (shape == null) {
            System.out.println("图形对象不能为空！");
            return;
        }
        double area = shape.getArea();
        System.out.printf("该图形的面积为：%.2f%n", area);
    }
}