在 JPanel 上使用滑块绘制二次公式答案

【问题标题】：Drawing the Quadratic formula with sliders on a JPanel在 JPanel 上使用滑块绘制二次公式
【发布时间】：2013-12-12 21:36:23
【问题描述】：

所以，我正在尝试制作一个程序，您可以在其中通过滑块输入二次公式 (ax^2+bx+c)。然后它会在您调整 A、B 和 C 时绘制图表。

问题：

我希望我用超级颜料和滑块写的东西放在一个地方。当我运行它时，滑块就位。有正确背景的空间，我希望面板中有我的图表，但没有实际图表。

这是我的驱动程序类：

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

public class quadraticslider
{

     public static void main (String[] args)
   {
      JFrame frame = new JFrame ("Quadratic Slider");
      frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

      frame.getContentPane().add(new pp109quadraticpanel());

      frame.pack();
      frame.setVisible(true);
   }
}

这是面板类：

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

public class quadraticpanel extends JPanel
{
   private JPanel controls, graphPanel;
   private JSlider ASlider, BSlider, CSlider;
   private JLabel ALabel, BLabel, CLabel;
   double A, B, C, x,Y;

  //
  //SLIDERS YO
  //
   public quadraticpanel()
   {
      ASlider = new JSlider (JSlider.HORIZONTAL, 0, 255, 0);
      ASlider.setMajorTickSpacing (50);
      ASlider.setMinorTickSpacing (10);
      ASlider.setPaintTicks (true);
      ASlider.setPaintLabels (true);
      ASlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      BSlider = new JSlider (JSlider.HORIZONTAL, 0, 255, 0);
      BSlider.setMajorTickSpacing (50);
      BSlider.setMinorTickSpacing (10);
      BSlider.setPaintTicks (true);
      BSlider.setPaintLabels (true);
      BSlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      CSlider = new JSlider (JSlider.HORIZONTAL, 0, 255, 0);
      CSlider.setMajorTickSpacing (50);
      CSlider.setMinorTickSpacing (10);
      CSlider.setPaintTicks (true);
      CSlider.setPaintLabels (true);
      CSlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      SliderListener listener = new SliderListener();
      ASlider.addChangeListener (listener);
      BSlider.addChangeListener (listener);
      CSlider.addChangeListener (listener);


      ALabel = new JLabel ("a: 0");
      ALabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      BLabel = new JLabel ("b: 0");
      BLabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      CLabel = new JLabel ("c: 0");
      CLabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      controls = new JPanel();
      BoxLayout layout = new BoxLayout (controls, BoxLayout.Y_AXIS);
      controls.setLayout (layout);
      controls.add (ALabel);
      controls.add (ASlider);
      controls.add (Box.createRigidArea (new Dimension (0, 20)));
      controls.add (BLabel);
      controls.add (BSlider);
      controls.add (Box.createRigidArea (new Dimension (0, 20)));
      controls.add (CLabel);
      controls.add (CSlider);



      graphPanel = new JPanel();
      graphPanel.setPreferredSize (new Dimension (500, 500));
      graphPanel.setBackground (Color.white);

      add (controls); 
      add (graphPanel);




   }   

    //Here I'm taking the equation, running it through -10 to 10
    //It takes the doubles from the equation, converts
    //it to int then draws the quadratic formula in dots.

     public void paintComponent(Graphics page)
   {  

     super.paintComponent (page);

     for ( x=-10; x <= 10; x++)
     {
         Y = (A*(Math.pow(x,2)))+(B*x)+(C);
         int g = (int)Math.round(x);
         int h = (int)Math.round(Y);
         page.setColor (Color.black);
          page.fillOval (g, h, 1, 1);
      }


    }


   public class SliderListener implements ChangeListener
   {
///
///Reads the user input via slider.
///

      public void stateChanged (ChangeEvent event)
      {
         A = ASlider.getValue();
         B = BSlider.getValue();
         C = CSlider.getValue();

         ALabel.setText ("a: " + A);
         BLabel.setText ("b: " + B);
         CLabel.setText ("c: " + C);

      }
   }
}

【问题讨论】：

没错，但sscce 总是一个好的开始。它显示了努力并允许人们专注于特定问题。
谢谢！我一直在努力让这个程序正常工作，哈哈。
sscce，排名第一的编程头痛药！
我喜欢这个程序。这是一个真正的头痛，但我喜欢这个结果。

标签： java swing compiler-errors jpanel

【解决方案1】：

这些使用JFreeChart 的examples 可能很有趣。如here 所示，您可以使用SwingWorker 为渲染设置动画，而此example 使用JSlider 更新图表。

附录：您的代码的这种变体可能会指导您继续前进。注意，

覆盖graphPanel 中的相关方法。
缩放和反转坐标，如图here。
考虑使用JSpinner 作为小数值。
使用常量来保持一致性。
为了清楚起见，使用通用命名约定。
另见Initial Threads。

import java.awt.*;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/** @see https://stackoverflow.com/a/20556929/230513 */
public class QuadraticSlider {

    private static final int N = 500;
    private static final int A = 1;
    private static final int B = 0;
    private static final int C = 0;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame("Quadratic Slider");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new QuadraticPanel());
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    private static class QuadraticPanel extends JPanel {

        private Box controls;
        private JPanel graphPanel;
        private JSlider aSlider, bSlider, cSlider;
        private JLabel aLabel, bLabel, cLabel;
        double a, b, c, x, y;

        public QuadraticPanel() {
            aSlider = new JSlider(JSlider.HORIZONTAL, -25, 25, A);
            aSlider.setMajorTickSpacing(10);
            aSlider.setMinorTickSpacing(5);
            aSlider.setPaintTicks(true);
            aSlider.setPaintLabels(true);
            aSlider.setAlignmentX(Component.LEFT_ALIGNMENT);

            bSlider = new JSlider(JSlider.HORIZONTAL, -10, 10, B);
            bSlider.setMajorTickSpacing(5);
            bSlider.setMinorTickSpacing(1);
            bSlider.setPaintTicks(true);
            bSlider.setPaintLabels(true);
            bSlider.setAlignmentX(Component.LEFT_ALIGNMENT);

            cSlider = new JSlider(JSlider.HORIZONTAL, -100, 100, C);
            cSlider.setMajorTickSpacing(50);
            cSlider.setMinorTickSpacing(10);
            cSlider.setPaintTicks(true);
            cSlider.setPaintLabels(true);
            cSlider.setAlignmentX(Component.LEFT_ALIGNMENT);

            SliderListener listener = new SliderListener();
            aSlider.addChangeListener(listener);
            bSlider.addChangeListener(listener);
            cSlider.addChangeListener(listener);

            aLabel = new JLabel("a: 0");
            bLabel = new JLabel("b: 0");
            cLabel = new JLabel("c: 0");
            controls = new Box(BoxLayout.Y_AXIS);
            controls.add(aLabel);
            controls.add(aSlider);
            controls.add(Box.createRigidArea(new Dimension(0, 20)));
            controls.add(bLabel);
            controls.add(bSlider);
            controls.add(Box.createRigidArea(new Dimension(0, 20)));
            controls.add(cLabel);
            controls.add(cSlider);

            graphPanel = new JPanel() {
                private static final int SCALE = 5;
                @Override
                public Dimension getPreferredSize() {
                    return new Dimension(N, N);
                }

                @Override
                public void paintComponent(Graphics g) {
                    super.paintComponent(g);
                    for (x = -10; x <= 10; x++) {
                        y = a * x * x + b * x + c;
                        g.setColor(Color.black);
                        int w = (int) (x * SCALE) + N / 2;
                        int h = (int) (-y * SCALE) + N / 2;
                        g.fillOval(w, h, 5, 5);
                    }
                }
            };
            graphPanel.setBackground(Color.white);

            add(controls);
            add(graphPanel);
            listener.stateChanged(null);
        }

        class SliderListener implements ChangeListener {

            @Override
            public void stateChanged(ChangeEvent event) {
                a = aSlider.getValue() / 5d;
                b = bSlider.getValue();
                c = cSlider.getValue();

                aLabel.setText("a: " + a);
                bLabel.setText("b: " + b);
                cLabel.setText("c: " + c);

                repaint();
            }
        }
    }
}

【讨论】：

我一直在努力工作，并且接近完成它。现在我遇到了某种编译器错误。
酷，我运行了代码，这正是我想要它做的。现在看看你改变了什么。什么是“EventQueue.invokeLater(new Runnable()”？“@Override”是什么意思？
另外，你除以 5d，为什么？ a = aSlider.getValue() / 5d;
@munchschair：快速获取小数值。
d 代表什么？它没有在任何地方声明。

【解决方案2】：

_"错误：可能损失精度 Y = (A*(Math.pow(x,2)))+(B*x)+(C); ^ required: int found: double"_

你所有的 int 变量int A, B, C, x,Y;。让他们doubles。 double A, B, C, x,Y;

【讨论】：

我在一分钟前打败了你，然后对变量进行了四舍五入，这样画起来更容易吗？我必须这样做吗，或者我可以画双打吗？无论如何，我从我的驱动程序类中运行它，它可以编译，但是当我运行它时什么都没有。
绘制时可以将 (int) 转换为变量。
我的双打被转换成整数。
"我从我的驱动程序类中运行它，它可以编译，但是当我运行它时没有任何反应。"。很可能；您的代码中还有其他问题。
@trashgod 实际上我今天刚刚下载了JFreeChart。以前从未使用过它，但我很高兴开始使用它。感谢您在整个网站上对它的“推广”！ :)

【解决方案3】：

我修改了代码，使它在给定 a b 和 c 的情况下求解 x。然后将 x 重新插入并求解 y。不过我还是没画出来。我还取出了循环，因为滑块正在设置导致 x 的 a b 和 c 值。有谁知道为什么不画吗？

package quadraticslider;

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

public class quadraticslider
{

     public static void main (String[] args)
   {
      JFrame frame = new JFrame ("Quadratic Slider");
      frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

      frame.getContentPane().add(new quadraticpanel());

      frame.pack();
      frame.setVisible(true);
   }
}

包装quadraticslider；

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

public class quadraticpanel extends JPanel
{
   private JPanel controls, graphPanel;
   private JSlider ASlider, BSlider, CSlider;
   private JLabel ALabel, BLabel, CLabel;
   double A, B, C, x,Y;


   public quadraticpanel()
   {
      ASlider = new JSlider (JSlider.HORIZONTAL, -25, 25, 0);
      ASlider.setMajorTickSpacing (50);
      ASlider.setMinorTickSpacing (10);
      ASlider.setPaintTicks (true);
      ASlider.setPaintLabels (true);
      ASlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      BSlider = new JSlider (JSlider.HORIZONTAL, -25, 25, 0);
      BSlider.setMajorTickSpacing (50);
      BSlider.setMinorTickSpacing (10);
      BSlider.setPaintTicks (true);
      BSlider.setPaintLabels (true);
      BSlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      CSlider = new JSlider (JSlider.HORIZONTAL, -25, 25, 0);
      CSlider.setMajorTickSpacing (50);
      CSlider.setMinorTickSpacing (10);
      CSlider.setPaintTicks (true);
      CSlider.setPaintLabels (true);
      CSlider.setAlignmentX (Component.LEFT_ALIGNMENT);

      SliderListener listener = new SliderListener();
      ASlider.addChangeListener (listener);
      BSlider.addChangeListener (listener);
      CSlider.addChangeListener (listener);


      ALabel = new JLabel ("a: 0");
      ALabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      BLabel = new JLabel ("b: 0");
      BLabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      CLabel = new JLabel ("c: 0");
      CLabel.setAlignmentX (Component.LEFT_ALIGNMENT);
      controls = new JPanel();
      BoxLayout layout = new BoxLayout (controls, BoxLayout.Y_AXIS);
      controls.setLayout (layout);
      controls.add (ALabel);
      controls.add (ASlider);
      controls.add (Box.createRigidArea (new Dimension (0, 20)));
      controls.add (BLabel);
      controls.add (BSlider);
      controls.add (Box.createRigidArea (new Dimension (0, 20)));
      controls.add (CLabel);
      controls.add (CSlider);



      graphPanel = new JPanel();
      graphPanel.setPreferredSize (new Dimension (500, 500));
      graphPanel.setBackground (Color.white);

      add (controls); 
      add (graphPanel);




   }   



     public void paintComponent(Graphics page)
   {  

     super.paintComponent (page);




         x = (-B + (Math.sqrt((B*B - ((4 * A * C))))))/ (2 * A);
         Y = (A*(Math.pow(x,2)))+(B*x)+(C);
         int g = (int)Math.round(x);
         int h = (int)Math.round(Y);
         page.setColor (Color.black);
         page.drawOval (g, h, 1, 1);



    }


   public class SliderListener implements ChangeListener
   {
///
///Reads the user input via slider.
///

      public void stateChanged (ChangeEvent event)
      {
         A = ASlider.getValue();
         B = BSlider.getValue();
         C = CSlider.getValue();

         ALabel.setText ("a: " + A);
         BLabel.setText ("b: " + B);
         CLabel.setText ("c: " + C);

      }

} }

【讨论】：

我编辑了它。它给出了指向最后一个加号的精度误差： Y = (A*(Math.pow(x,2)))+(B*x)+(C) 我尝试在等式后对数字进行四舍五入，但没有效果。它指向方程。
有人知道为什么它不画吗？见answer。