java - 尝试划分颜色来绘制彩虹 donut

Question

板级:

import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.geom.Ellipse2D;
import javax.swing.JPanel;

public class Board extends JPanel {

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);

    super.setBackground(Color.BLACK);
    drawDonut(g, Color.WHITE);
}

private void drawDonut(Graphics g, Color c) {

    Graphics2D g2d = (Graphics2D) g;

    RenderingHints rh
            = new RenderingHints(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

    rh.put(RenderingHints.KEY_RENDERING,
            RenderingHints.VALUE_RENDER_QUALITY);

    g2d.setRenderingHints(rh);

    Dimension size = getSize();
    double w = size.getWidth();
    double h = size.getHeight();

    Ellipse2D e = new Ellipse2D.Double(0, 0, 160, 260);
    g2d.setStroke(new BasicStroke(3));

    //RainbowColors rb = new RainbowColors(6);

    for (double deg = 0; deg < 360; deg += 5) {
        AffineTransform at
                = AffineTransform.getTranslateInstance(w/2, h/2);
        at.rotate(Math.toRadians(deg));

        g2d.setColor(Color.RED/*rb.getNewColor()*/);
        g2d.draw(at.createTransformedShape(e));
    }
  }
}

当我启动这个程序时，我的屏幕上首先出现白色圆​​圈，其余为紫色。我做了一些调试，并在控制台程序中从“RainbowColors”类的构造函数写入了两次消息

但是该对象只生成一次。

Answer 1

给定正确的颜色生成逻辑(RainbowColors 类)，Board 类就可以正常工作:

class Board extends JPanel {

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        super.setBackground(Color.BLACK);
        drawDonut(g, Color.WHITE);
    }

    private void drawDonut(Graphics g, Color c) {

        Graphics2D g2d = (Graphics2D) g;

        RenderingHints rh = new RenderingHints(RenderingHints.KEY_ANTIALIASING,
                                                RenderingHints.VALUE_ANTIALIAS_ON);
        rh.put(RenderingHints.KEY_RENDERING,
                RenderingHints.VALUE_RENDER_QUALITY);
        g2d.setRenderingHints(rh);

        Dimension size = getSize();
        double w = size.getWidth();
        double h = size.getHeight();

        Ellipse2D e = new Ellipse2D.Double(0, 0, 160, 260);
        g2d.setStroke(new BasicStroke(3));

        double range = 360, step = 5;
        RainbowColors rb = new RainbowColors((int)(range/step));

        for (double deg = 0; deg < range; deg += step) {
            AffineTransform at = AffineTransform.getTranslateInstance(w/2, h/2);
            at.rotate(Math.toRadians(deg));
            g2d.setColor(rb.getNewColor());
            g2d.draw(at.createTransformedShape(e));
        }
    }
}

class RainbowColors {

    private static final int DEFAULT_NUMBER_OF_COLORS = 100;
    private final int numberOfColors;
    private int index;
    private Color[] colors;

    RainbowColors() {
        this(DEFAULT_NUMBER_OF_COLORS);
    }

    RainbowColors(int numberOfColors) {
        this.numberOfColors = numberOfColors > 0 ?  numberOfColors : DEFAULT_NUMBER_OF_COLORS;
        makeColors();
    }

    //based on https://stackoverflow.com/a/22973823/3992939
    private void makeColors() {

        int range =  numberOfColors / 6;  //6 for loops, each changes R G or B
        int step = 255/range;

        List<Color> colorsList = new ArrayList<>();
        for (int r=0; r< range; r++) {
            colorsList.add(new Color(r*step,    255,     0));
        }
        for (int g=range; g>0; g--) {
            colorsList.add(new Color(   255, g*step,     0));
        }
        for (int b=0; b<range; b++) {
            colorsList.add(new Color(   255,     0, b*step));
        }
        for (int r=range; r>0; r--) {
            colorsList.add(new Color(r*step,       0,  255));
        }
        for (int g=0; g<range; g++) {
            colorsList.add(new Color(      0, g*step,   255));
        }
        for (int b=range; b>0; b--) {
            colorsList.add(new Color(      0,    255, b*step));
        }

        colors = colorsList.toArray(new Color[colorsList.size()]);
    }

    Color getNewColor() {
        index = index >= colors.length ? 0 : index;
        return colors[index++];
    }
}

可以从 here 复制 mcve .