Question

目前我正在关注一本书，本章将简要介绍一下GUI。

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

/**
The MetricConverterWindow class lets the user enter a
distance in kilometers. Radio buttons can be selected to
convert the kilometers to miles, feet, or inches.
*/

public class MetricConverterWindow extends JFrame
{
private JPanel panel;                  // A holding panel
private JLabel messageLabel;           // A message to the user
private JTextField kiloTextField;      // To hold user input
private JRadioButton milesButton;      // To convert to miles
private JRadioButton feetButton;       // To convert to feet
private JRadioButton inchesButton;     // To convert to inches
private ButtonGroup radioButtonGroup;  // To group radio buttons
private final int WINDOW_WIDTH = 400;  // Window width
private final int WINDOW_HEIGHT = 100; // Window height

/**
  Constructor
*/

public MetricConverterWindow()
{
  // Set the title.
  setTitle("Metric Converter");

  // Set the size of the window.
  setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

  // Specify an action for the close button.
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

  // Build the panel and add it to the frame.
  buildPanel();

  // Add the panel to the frame's content pane.
  add(panel);

  // Display the window.
  setVisible(true);
}

/**
  The buildPanel method adds a label, text field, and
  and three buttons to a panel.
*/

private void buildPanel()
{
  // Create the label, text field, and radio buttons.
  messageLabel = new JLabel("Enter a distance in kilometers");
  kiloTextField = new JTextField(10);
  milesButton = new JRadioButton("Convert to miles");
  feetButton = new JRadioButton("Convert to feet");
  inchesButton = new JRadioButton("Convert to inches");

  // Group the radio buttons.
  radioButtonGroup = new ButtonGroup();
  radioButtonGroup.add(milesButton);
  radioButtonGroup.add(feetButton);
  radioButtonGroup.add(inchesButton);

  // Add action listeners to the radio buttons.
  milesButton.addActionListener(new RadioButtonListener());
  feetButton.addActionListener(new RadioButtonListener());
  inchesButton.addActionListener(new RadioButtonListener());

  // Create a panel and add the components to it.
  panel = new JPanel();
  panel.add(messageLabel);
  panel.add(kiloTextField);
  panel.add(milesButton);
  panel.add(feetButton);
  panel.add(inchesButton);
}

/**
  Private inner class that handles the event when
  the user clicks one of the radio buttons.
*/

private class RadioButtonListener implements ActionListener
{
  public void actionPerformed(ActionEvent e)
  {
     String input;          // To hold the user's input
     String convertTo = ""; // The units we're converting to
     double result = 0.0;   // To hold the conversion

     // Get the kilometers entered.
     input = kiloTextField.getText();

     // Determine which radio button was clicked.
     if (e.getSource() == milesButton)
     {
        // Convert to miles.
        convertTo = " miles.";
        result = Double.parseDouble(input) * 0.6214;
     }
     else if (e.getSource() == feetButton)
     {
        // Convert to feet.
        convertTo = " feet.";
        result = Double.parseDouble(input) * 3281.0;
     }
     else if (e.getSource() == inchesButton)
     {
        // Convert to inches.
        convertTo = " inches.";
        result = Double.parseDouble(input) * 39370.0;
     }

     // Display the conversion.
     JOptionPane.showMessageDialog(null, input + 
              " kilometers is " + result + convertTo);
  }
 }

/**
  The main method creates an instance of the
  MetricConverterWindow class, displaying its window.
*/

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

这是本书的直接例子。我最初在一个名为window的包中加入了一些其他与GUI相关的类。我决定将其移至默认值以测试某些内容。到目前为止，我只是导入了javax.swing。*而不是专门的javax.swing.JOptionPane，这完全是因为到目前为止这本书已经完成了GUI示例。当我从窗口包中删除它并将其移动到默认包时，我得到错误“方法showMessageDialog（null，String）未定义类型JOptionPane”。如果我将它添加回我的包中以获取我制作的GUI示例，我没有问题。我试图用我能想到的每一种方式来说出来，但是我找不到解决方案，为什么一旦从包中删除它就会出现错误。

我意识到我并没有达到我想要问的程度。我想弄清楚的是我需要导入两者吗？

表示它在包中工作正常没有意义。但是在默认情况下它会产生错误。

导入javax.swing.JOptionPane

0 个答案: