用java代码用for循环画几个画布为黑色，像素为800*480的，三角形为白色，并且保存到自定义的文件夹里

以下是用Java代码使用for循环画黑色画布、白色三角形并保存到自定义文件夹的示例代码：

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class DrawCanvas {
    public static void main(String[] args) {
        int width = 800;
        int height = 480;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = image.createGraphics();
        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, width, height);
        g2d.setColor(Color.WHITE);
        int[] xPoints = {width/2, 0, width};
        int[] yPoints = {0, height, height};
        Polygon triangle = new Polygon(xPoints, yPoints, 3);
        g2d.fill(triangle);
        g2d.dispose();
        File output = new File("custom_folder/canvas.png");
        try {
            ImageIO.write(image, "png", output);
            System.out.println("Image saved to " + output.getAbsolutePath());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

请注意，您需要在代码中将“custom_folder”替换为您要保存图像的实际文件夹路径。