在JPanel上创建条形图

Question

谁能告诉我这有什么问题？我是Java的新手,我似乎无法理解为什么这不会打开JPanel或矩形或字符串.什么都没有显示,但它确实编译.

码:

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

public class Graphing extends JPanel
{

   public static void main (String[] args)
   {
   }

   public Graphing()
   {
      JFrame frame = new JFrame ("Nested Panels");
      frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

      frame.getContentPane();
      frame.setPreferredSize(new Dimension(350,200));
      frame.pack();
      frame.setVisible(true);
   }

   public void paintComponent (Graphics page)
   {            
      super.paintComponent (page);          
      final int HEIGHT = 10;

      page.setColor (Color.yellow);
      page.fillRect (50, 50, (7*10), HEIGHT);//1-10
      page.fillRect (50, 64, (5*10), HEIGHT);//11-20
      page.fillRect (50, 78, (0*10), HEIGHT);//21-30
      page.fillRect (50, 92, (1*10), HEIGHT);//31-40
      page.fillRect (50, 106, (9*10), HEIGHT);//41-50
      page.fillRect (50, 120, (12*10), HEIGHT);//51-60
      page.fillRect (50, 134, (4*10), HEIGHT);//61-70
      page.fillRect (50, 148, (6*10), HEIGHT);//71-80
      page.fillRect (50, 162, (2*10), HEIGHT);//81-90
      page.fillRect (50, 176, (13*10), HEIGHT);//91-100

      page.drawString("1-10",10,60);
      page.drawString("11-20",10,74);
      page.drawString("21-30",10,88);
      page.drawString("31-40",10,102);
      page.drawString("41-50",10,116);
      page.drawString("51-60",10,130);
      page.drawString("61-70",10,144);
      page.drawString("71-80",10,158);
      page.drawString("81-90",10,172);
      page.drawString("91-100",10,186);

      page.drawString("7", 30, 60);
      page.drawString("5", 30, 74);
      page.drawString("0", 30, 88);
      page.drawString("1", 30, 102);
      page.drawString("9", 30, 116);
      page.drawString("12", 30, 130);
      page.drawString("4", 30, 144);
      page.drawString("6", 30, 158);
      page.drawString("2", 30, 172);
      page.drawString("13", 30, 186);
   }

}

Answer 1

public Graphing()   {
  JFrame frame = new JFrame ("Nested Panels");
  frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

  frame.getContentPane().add(this);

在主要

public static void main(String[] args) {
    new Graphing();
} 

要完全犹太洁食,主要方法应该是:

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
           new Graphing();
        }
    });
} 

虽然在这一点上,您不必知道第二个主要方法代码的细节,但确实知道它确保在主Swing线程上调用Swing GUI.这样做有助于避免在您的简单程序中不太可能发生的不可预测的线程问题,但如果您的代码变得更复杂,则可能会发生这种问题.

其他问题 - 您将尝试避免使用魔术数字,硬编码数字,而是使用变量,这将允许您更轻松地更改条形的高度.