java在流布局中看不到任何内容

Question

到目前为止，我编写了一个应用程序，它只显示小部件，以便在添加操作侦听器等之前查看是否一切正常

问题是当我运行它时，什么都没有显示，只有一个空白屏幕

我附上了布局应该是什么样子的图片。我是这个网站的新手，所以很明显，在10点之前我不能发布任何图片。这里有一个到PhotoBucket的链接

http://i930.photobucket.com/albums/ad149/Wolverino5/pic_zpsa4599592.png

这是到目前为止我的代码

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


public class Project9 extends JFrame
{
   private JTextField idLabel;
   private JTextField idField;
   private JTextField priceLabel;
   private JTextField priceField;
   private JTextField numInStockLabel;
   private JTextField numInStockField;
   private JTextField codeLabel;
   private JTextField codeField;
   private JTextField transaction;

   private JButton insert;
   private JButton delete;
   private JButton display;
   private JButton displayOne;
   private JButton hide;
   private JButton clear;

   private Container c = getContentPane();

   public static void main(String[] args)
   {
   JFrame frame = new JFrame();
   frame.setSize(650,700);
   frame.setVisible(true);
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

   }


   public Project9()
   {
   setTitle("BOOK DataBase Application");
   c.setLayout(new FlowLayout());
   Label main = new Label("Data Entry: Best Bargian Book Store");
   c.add(main);
   idLabel = new JTextField("Enter ID",15);
   idLabel.setEditable(false);
   c.add(idLabel);
   idField = new JTextField();
   c.add(idField);
   priceLabel = new JTextField("Enter Price:",15);
   priceLabel.setEditable(false);
   c.add(priceLabel);
   priceField = new JTextField();
   c.add(priceField);
   numInStockLabel = new JTextField("Enter Number In Stock:",15);
   numInStockLabel.setEditable(false);
   c.add(numInStockLabel);
   numInStockField = new JTextField();
   c.add(numInStockField);
   codeLabel = new JTextField("Enter Code: 1,2,3 or 4:",15);
   codeLabel.setEditable(false);
   c.add(codeLabel);
   codeField = new JTextField();
   c.add(codeField);
   insert = new JButton("Insert");
   c.add(insert);
   delete = new JButton("Delete");
   c.add(delete);
   display = new JButton("Display");
   c.add(display);
   displayOne = new JButton("displayOne");
   c.add(displayOne);
   hide = new JButton("Hide");
   c.add(hide);
   clear = new JButton("Clear");
   c.add(clear);
   Label messages = new Label ("Messages");
   c.add(messages);
   transaction = new JTextField();
   c.add(transaction);


   }
}

Answer 1

您永远不会创建Project9类的实例，因此运行的四行是main中创建空JFrame的四行

更改：

JFrame frame = new JFrame();

致：

JFrame frame = new Project9();