Question

我有一个带按钮的代码。按下按钮时，圆圈会随机出现在颜色随机的位置。只能有10个圆圈。

现在我添加了随机颜色功能，问题是在绘制每个圆圈后，它的颜色开始变得无用。

我怎样才能让颜色不变？

class Panel extends JPanel  {

    private JButton button;
    private Ellipse2D.Double[] circles;
    Integer count;


    public Panel()  {
            setup();
    }

    private void setup()  {
            count=new Integer(0);
            circles=new Ellipse2D.Double[10];
            button=new JButton(count.toString());
            button.addActionListener(new ActionListener() {
               @Override
               public void actionPerformed(ActionEvent e) {
                            Random r=new Random();
                            //position circles with diameter 100 in a way 
                            //that it would fit in a window's size
                            int highX=getWidth()-100;
                            int highY=getHeight()-100;
                            circles[count]=new 
                                     Ellipse2D.Double(r.nextInt(highX), 
                                          r.nextInt(highY), 100, 100);
                            count++;

                            button.setText(count.toString());
                    }
                });

          add(button);
        }


    public void paintComponent(Graphics g)  {
            super.paintComponent(g);
            paintStuff(g);
            repaint(); 
        }

    private void paintStuff(Graphics g)  {
            Graphics2D g2=(Graphics2D) g;
            g2.setPaint(Color.RED);

            if (count!=0)  {
                for (int i=0; i<count; i++)  {
                        g2.draw(circles[i]);
                        Random r=new Random();
                        int red=r.nextInt(256);
                        int green=r.nextInt(256);
                        int blue=r.nextInt(256);
                        g2.setPaint(new Color(red, green, blue));
                        g2.fill(circles[i]);
                }
            }
    }
}

public class Frame extends JFrame  {
     private Panel panel;
     public Frame()  {
        panel=new Panel();
        add(panel);
     }

     public static void main(String[] args)  {
          Frame frame=new Frame();
     }
}

Answer 1

永远不要在绘画方法中调用重绘，因为这会导致“穷人”＃34;动画发生。而是在JButton的ActionListener中调用它。此外，不要在绘画方法中随机化，而是在ActionListener中执行此操作。绘画方法不在您的控制之下，您不想用它来改变对象的状态，而只是为了显示它。

其他建议：

您的代码仍然需要设置JFrame的setDefaultCloseOperation
仍然需要设置JFrame可见
您从不建议在代码中调整大小。我自己，我建议覆盖你的JPanel的public Dimension getPreferredSize()并在添加JPanel之后但在显示它之前在JFrame上调用pack()。
我重命名您的课程，以便这些名称不会与核心Java课程发生冲突，并导致您的教师，我们或您未来的自我混淆。
不要在for循环中继续重新创建一个新的Random对象。相反，为什么不简单地给类一个随机字段，创建一次，但重复使用该对象。
您需要将颜色与形状/ Ellipse2D相关联。对于一对一的通信，请考虑使用地图，例如HashMap<Shape, Color>。

例如：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.geom.Ellipse2D;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;

import javax.swing.*;

@SuppressWarnings("serial")
public class Panel2 extends JPanel {
    // preferred size constants
    private static final int PREF_W = 600;
    private static final int PREF_H = PREF_W;

    // map to hold circles and colors
    private Map<Shape, Color> shapeColorMap = new LinkedHashMap<>();

    public Panel2() {
        add(new JButton(new RandomColorAction()));
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        // create *smooth* drawings
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        paintStuff(g2);
    }

    private void paintStuff(Graphics2D g2) {
        // iterate through our map extracting all circles and colors
        // and drawing them
        for (Entry<Shape, Color> entry : shapeColorMap.entrySet()) {
            Shape shape = entry.getKey();
            Color color = entry.getValue();
            g2.setColor(color);
            g2.fill(shape);
        }
    }

    // listener for our button
    private class RandomColorAction extends AbstractAction {
        private static final int CIRC_WIDTH = 100;
        private Random random = new Random();
        private int count = 0;

        public RandomColorAction() {
            super("Random Circle: 0");
            putValue(MNEMONIC_KEY, KeyEvent.VK_R);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // create our random ellipses
            int x = random.nextInt(getWidth() - CIRC_WIDTH);
            int y = random.nextInt(getHeight() - CIRC_WIDTH);
            Shape shape = new Ellipse2D.Double(x, y, CIRC_WIDTH, CIRC_WIDTH);

            // create our random color using HSB for brighter colors
            float hue = random.nextFloat();
            float saturation = (float) (0.8 + random.nextFloat() * 0.2);
            float brightness = (float) (0.8 + random.nextFloat() * 0.2);
            Color color = Color.getHSBColor(hue, saturation, brightness);
            shapeColorMap.put(shape, color);

            // increment count, place items into map, repaint
            count++;
            putValue(NAME, "Random Circle: " + count);
            repaint();
        }
    }

    private static void createAndShowGui() {
        Panel2 mainPanel = new Panel2();

        JFrame frame = new JFrame("Panel2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

在评论中，Camickr敏锐地指出：

绘制方法应绘制组件的当前状态。通过使用HashMap，您可以引入随机性的可能性。无法保证通过地图的迭代顺序。因此，当新条目添加到地图时，每个Shape的绘制顺序可能会发生变化。一般不是问题，但如果两个随机形状重叠，那么结果就是翻转，这种形状是相互重叠的。

当然，他是完全正确的，因为没有保证HashMap的顺序。幸运的是，变量本身被声明为Map类型，因此为了保持顺序，所有人需要做的是将实际的对象类型从HashMap更改为LinkedHashMap，这是一个每its API的类：

此实现使客户端免受HashMap（和Hashtable）提供的未指定的，通常混乱的排序，而不会导致与TreeMap相关的成本增加。

因此，对于TLDR，请更改：

private Map<Shape, Color> shapeColorMap = new HashMap<>();

到此：

private Map<Shape, Color> shapeColorMap = new LinkedHashMap<>();

修改了颜色计算。

只是为了它的乐趣，它引入Path2D和AffineTransform与MouseListener / MouseMotionListener以允许拖动圆圈：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.AffineTransform;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Path2D;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;
import java.util.Set;

import javax.swing.*;

@SuppressWarnings("serial")
public class Panel2 extends JPanel {
    // preferred size constants
    private static final int PREF_W = 600;
    private static final int PREF_H = PREF_W;

    // map to hold circles and colors
    private Map<Shape, Color> shapeColorMap = new LinkedHashMap<>();

    public Panel2() {
        add(new JButton(new RandomColorAction()));
        MyMouse myMouse = new MyMouse();
        addMouseListener(myMouse);
        addMouseMotionListener(myMouse);
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        // create *smooth* drawings
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        paintStuff(g2);
    }

    private void paintStuff(Graphics2D g2) {
        // iterate through our map extracting all circles and colors
        // and drawing them
        for (Entry<Shape, Color> entry : shapeColorMap.entrySet()) {
            Shape shape = entry.getKey();
            Color color = entry.getValue();
            g2.setColor(color);
            g2.fill(shape);
        }
    }

    private class MyMouse extends MouseAdapter {
        private Entry<Shape, Color> selected = null;
        private Path2D path;
        private Point p = null;

        @Override
        public void mousePressed(MouseEvent e) {
            Set<Entry<Shape, Color>> entrySet = shapeColorMap.entrySet();
            // get Shape pressed
            for (Entry<Shape, Color> entry : entrySet) {
                if (entry.getKey().contains(e.getPoint())) {
                    selected = entry;
                }
            }

            if (selected != null) {
                path = new Path2D.Double(selected.getKey());
                // move it to the top
                entrySet.remove(selected);
                shapeColorMap.put(path, selected.getValue());

                p = e.getPoint();
                repaint();
            }
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            if (selected != null) {
                moveSelected(e);
            }
            selected = null;
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            if (selected != null) {
                moveSelected(e);
            }
        }

        private void moveSelected(MouseEvent e) {
            int x = e.getX() - p.x;
            int y = e.getY() - p.y;
            p = e.getPoint();

            AffineTransform at = AffineTransform.getTranslateInstance(x, y);
            path.transform(at);
            repaint();
        }
    }

    // listener for our button
    private class RandomColorAction extends AbstractAction {
        private static final int CIRC_WIDTH = 100;
        private Random random = new Random();
        private int count = 0;

        public RandomColorAction() {
            super("Random Circle: 0");
            putValue(MNEMONIC_KEY, KeyEvent.VK_R);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            // create our random ellipses
            int x = random.nextInt(getWidth() - CIRC_WIDTH);
            int y = random.nextInt(getHeight() - CIRC_WIDTH);
            Shape shape = new Ellipse2D.Double(x, y, CIRC_WIDTH, CIRC_WIDTH);

            // create our random color using HSB for brighter colors
            float hue = random.nextFloat();
            float saturation = (float) (0.8 + random.nextFloat() * 0.2);
            float brightness = (float) (0.8 + random.nextFloat() * 0.2);
            Color color = Color.getHSBColor(hue, saturation, brightness);
            shapeColorMap.put(shape, color);

            // increment count, place items into map, repaint
            count++;
            putValue(NAME, "Random Circle: " + count);
            repaint();
        }
    }

    private static void createAndShowGui() {
        Panel2 mainPanel = new Panel2();

        JFrame frame = new JFrame("Panel2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

Answer 2

paintStuff(Graphics g);

多次调用，每次刷新圆形颜色。这是设置颜色的错误位置，您需要在添加圆圈时进行设置。

创建一个java.awt.Color数组作为全局变量

private Color[] circlesColors;

然后只需在actionPerformed(...)方法中填充此数组。这是带有更改的setup方法

private void setup()  {
    count=new Integer(0);
    circles=new Ellipse2D.Double[10];
    circlesColors = new Color[10]; //Init the colors array to the same size of circles array
    button=new JButton(count.toString());
    button.addActionListener(new ActionListener() {
       @Override
       public void actionPerformed(ActionEvent e) {
          Random r=new Random();

          int highX=getWidth()-100;
          int highY=getHeight()-100;

          circles[count]=new Ellipse2D.Double(r.nextInt(highX), r.nextInt(highY), 100, 100);
          circlesColors[count] = new Color(r.nextInt(256), r.nextInt(256), r.nextInt(256)); //Assign random color 
          count++;

          button.setText(count.toString());
      }
   });

   add(button);
}

然后在您的paint(...)方法

中

private void paintStuff(Graphics g)  {
     Graphics2D g2=(Graphics2D) g;
     g2.setPaint(Color.RED);

     if (count!=0)  {
         for (int i=0; i<count; i++)  {
             g2.draw(circles[i]);
             g2.setPaint(circlesColors[i]); //Get and set the color associated to the circle 
             g2.fill(circles[i]);
         }
     }
}

用随机颜色填充对象

2 个答案: