使用Java三角函数结合AWT库根据边角参数绘制三角形求助

实现方案 #

坐标计算逻辑 #

• 固定三角形第一个顶点A的坐标为(300, 600)作为绘制基准，避免图形超出画布范围
• 将输入的已知边s1设为水平向右的边，因此第二个顶点B的坐标直接为(300 + s1, 600)
• 第三个顶点C的坐标通过极坐标转换计算：注意AWT画布的Y轴是向下增长的，因此垂直方向计算时需要对正弦值取反，公式如下：

  C点x坐标 = 300 + s3 * Math.cos(Math.toRadians(a1))
  C点y坐标 = 600 - s3 * Math.sin(Math.toRadians(a1))
  

代码修改说明 #

1. 组件初始化时自动调用calc方法获取用户输入的三角形参数
2. 修复原代码中三角函数计算时角度、弧度转换错误的问题
3. 第三边计算改用正弦定理，简化逻辑降低计算误差
4. 移除无返回值不生效的Math.toDegrees调用

完整可运行代码 #

import javax.swing.*;
import java.awt.*;

public class TriangleDrawProgram {
    public static void main (String[] args) {
        JFrame frame = new JFrame();
        CustomPaintComponent c = new CustomPaintComponent();
        frame.add(c);
        frame.setSize(1000,1000);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setTitle("Triangle");
        frame.setVisible(true);
    }
}

class CustomPaintComponent extends Component {
    private Triangle triangle;

    // 构造组件时触发参数输入
    public CustomPaintComponent() {
        triangle = calc();
    }

    public void paint(Graphics g){
        Graphics2D G2D = (Graphics2D)g;
        // 基准点A坐标
        int ax = 300;
        int ay = 600;
        // 点B坐标，s1水平向右
        int bx = (int) (ax + triangle.s1);
        int by = ay;
        // 点C坐标计算
        int cx = (int) (ax + triangle.s3 * Math.cos(Math.toRadians(triangle.a1)));
        int cy = (int) (ay - triangle.s3 * Math.sin(Math.toRadians(triangle.a1)));

        int[] xpoints = {ax, bx, cx};
        int[] ypoints = {ay, by, cy};
        G2D.drawPolygon(xpoints, ypoints, 3);
    }

    public Triangle calc(){
        double s1,a1,a2;
        s1 = Integer.parseInt(JOptionPane.showInputDialog("Please enter side 1"));
        a1 = Integer.parseInt(JOptionPane.showInputDialog("Please enter angle 1"));
        a2 = Integer.parseInt(JOptionPane.showInputDialog("Please enter angle 2"));
        // 计算第三个角
        double a3 = 180 - (a1 + a2);
        // 用正弦定理计算另外两条边，逻辑更简单
        double sinA1 = Math.sin(Math.toRadians(a1));
        double s2 = s1 * Math.sin(Math.toRadians(a2)) / sinA1;
        double s3 = s1 * Math.sin(Math.toRadians(a3)) / sinA1;

        System.out.println("side 1 is " + s1 + " side 2 is " + s2 + " side 3 is " + s3 + " and the third angle is: " + a3);
        return new Triangle(s1,s2,s3,a1,a2,a3);
    }
}

class Triangle{
    double s1,s2,s3,a1,a2,a3;

    Triangle(double s1, double s2, double s3, double a1, double a2, double a3){
        this.s1 = s1;
        this.s2 = s2;
        this.s3 = s3;
        this.a1 = a1;
        this.a2 = a2;
        this.a3 = a3;
    }
}

使用说明 #

运行程序后依次输入第一条边的长度（建议输入200-400之间的值避免超出画布）、第一个角、第二个角即可自动绘制对应三角形。

内容的提问来源于stack exchange，提问作者Leon Fardell