java计算不同图形面积代码

以下是Java计算不同图形面积的示例代码：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("请选择要计算面积的图形：");
        System.out.println("1. 正方形");
        System.out.println("2. 长方形");
        System.out.println("3. 圆形");
        System.out.println("4. 三角形");

        int choice = scanner.nextInt();

        switch (choice) {
            case 1:
                System.out.println("请输入正方形的边长：");
                double squareSide = scanner.nextDouble();
                double squareArea = squareSide * squareSide;
                System.out.println("正方形的面积为：" + squareArea);
                break;

            case 2:
                System.out.println("请输入长方形的长度：");
                double rectangleLength = scanner.nextDouble();
                System.out.println("请输入长方形的宽度：");
                double rectangleWidth = scanner.nextDouble();
                double rectangleArea = rectangleLength * rectangleWidth;
                System.out.println("长方形的面积为：" + rectangleArea);
                break;

            case 3:
                System.out.println("请输入圆形的半径：");
                double radius = scanner.nextDouble();
                double circleArea = Math.PI * radius * radius;
                System.out.println("圆形的面积为：" + circleArea);
                break;

            case 4:
                System.out.println("请输入三角形的底边长度：");
                double base = scanner.nextDouble();
                System.out.println("请输入三角形的高：");
                double height = scanner.nextDouble();
                double triangleArea = 0.5 * base * height;
                System.out.println("三角形的面积为：" + triangleArea);
                break;

            default:
                System.out.println("无效选择！");
        }

        scanner.close();
    }
}

该程序会通过键盘输入让用户选择要计算面积的图形类型，然后根据用户的选择分别计算不同图形的面积并输出结果。