为什么我们需要在 Swing 应用程序中扩展 JFrame?

2022-01-24 00:00:00 java swing jframe

为什么我们在构建 Swing 应用程序时需要扩展 JFrame 类.据我所知 extends 用于继承基类.JFrame 类的所有功能均未在以下程序中使用，但仍对其进行了扩展.我知道我错过了一些信息.是不是JFrame类的一些功能在后台运行.

Why do we need to extend the JFrame class when building a Swing application. As far as I know extends is used for inheriting the base class. None of the functions of the JFrame class are used in the following program but still it is extended. I know I am missing out on some information. Is it like some of the functions of JFrame class are running in the background.

1) 代码

import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JPasswordField;
import javax.swing.JOptionPane;

public class tuna extends JFrame{

   private JTextField item1;
   private JTextField item2;
   private JTextField item3;
   private JPasswordField passwordField;
   Container contentPane ;
   public tuna(){
      super("The title");

      setLayout(new FlowLayout());

      item1 = new JTextField(10);
      contentPane.add(item1);

      item2 = new JTextField("enter text here");
      add(item2);

      item3 = new JTextField("uneditable", 20);
      item3.setEditable(false);
      add(item3);

      passwordField = new JPasswordField("mypass");
      add(passwordField);

      thehandler handler = new thehandler();

      item1.addActionListener(handler);
      item2.addActionListener(handler);
      item3.addActionListener(handler);
      passwordField.addActionListener(handler);
   }

   public static void main(String[] args){
      tuna aye = new tuna();
   }

   private class thehandler implements ActionListener{

      public void actionPerformed(ActionEvent event){
         String string = "";

         if(event.getSource()==item1)
            string=String.format("field 1: %s",event.getActionCommand());
         else if (event.getSource()==item2)
            string=String.format("field 2: %s",event.getActionCommand());
         else if (event.getSource()==item3)
            string=String.format("field 3: %s",event.getActionCommand());
         else if (event.getSource()==passwordField)
            string=String.format("password field is: %", event.getActionCommand());
      }
   }
}

推荐答案

您不需要扩展 JFrame，事实上，我们中的许多人都在使用 Swing 编程，这很重要不是扩展这个类.我自己，我尝试扩展我计划改变类的固有行为的类——即覆盖类的非静态方法之一.由于我很少需要为 JFrame 执行此操作，因此我很少想要扩展它.

You don't need to extend JFrame and in fact many of us who do a lot of Swing programming make it a point not to extend this class. Myself, I try to extend classes where I plan on altering the innate behavior of the class -- i.e., override one of the non-static methods of the class. Since I rarely have to do this for a JFrame, I'll rarely want to extend it.

避免扩展它的另一个原因是:如果您稍后想在 JDialog 或 JOptionPane 或另一个容器中显示您刚刚创建的 GUI 作为复杂 GUI 的一部分，该怎么办?如果你的类扩展了 JFrame，这将很难做到.我自己，我尝试将我的 GUI 类用于创建 JPanel，以便更容易做到.

Another reason to avoid extending it: what if you later want to display the GUI you've just created in a JDialog or a JOptionPane or in another container as part of a complex GUI? If your class extends JFrame this will be hard to do. Myself, I try to gear my GUI classes towards creating JPanels so that this is much easier to do.

基于您的代码的愚蠢示例:

A silly example based on your code:

import javax.swing.*;

// this guy extends *nothing*
public class TunaExample {
   private static final int COLS = 10;
   private JPanel mainPanel = new JPanel(); // this is what I'll add to contentPane
   private JTextField field1 = new JTextField(COLS);
   private JTextField field2 = new JTextField(COLS);
   private JPasswordField passwordField = new JPasswordField(COLS);
   private JComponent[] allComponents = { new JLabel("Field 1:"), field1,
         new JLabel("Field 2:"), field2, new JLabel("Password:"), passwordField };

   public TunaExample() {
      field2.setEditable(false);
      field2.setFocusable(false);
      field1.setText("Field 1");
      field2.setText("Uneditable");

      for (JComponent comp : allComponents) {
         mainPanel.add(comp);
      }
   }

   public JComponent getMainComponent() {
      return mainPanel;
   }

   private static void createAndShowGui() {
      TunaExample tunaExample = new TunaExample();

      // creating my JFrame only when I need it and where I need it
      JFrame frame = new JFrame("Tuna Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(tunaExample.getMainComponent());
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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

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