converttempone.java

《A first book of java》by Gary J.Bronson 北大出版社

import java.text.*;  // need this for formatting
import javax.swing.*;
import java.awt.event.*;
import java.awt.Container;  // need this to add controls
import java.awt.*;  // need this for layout manager

public class ConvertTempOne extends JFrame
{
  private JFrame mainFrame;
  private JButton convertButton;
  private JButton exitButton;
  private JTextField fahrField;
  private JTextField celsField;
  private JLabel fahrLabel;
  private JLabel celsLabel;
 
  public ConvertTempOne() // a constructor
  {
    mainFrame = new JFrame("Temperature Conversion");

      // create all components
    convertButton = new JButton("Convert to Celsius");  
    exitButton = new JButton("Exit");
    fahrLabel = new JLabel("Enter a Fahrenheit temperature:");
    celsLabel = new JLabel("The corresponding Celsius value is:");
    fahrField = new JTextField(5);
    celsField = new JTextField(5);

      // get the content pane 
    Container c = mainFrame.getContentPane(); 
      // set the layout managare
    c.setLayout(new FlowLayout());
    
      // add the components to the ContentPane 
    c.add(fahrLabel);
    c.add(fahrField);
    c.add(celsLabel);
    c.add(celsField);
    c.add(convertButton);
    c.add(exitButton);
    
      // create accelerator keys
    convertButton.setMnemonic('C');
    exitButton.setMnemonic('x');

    mainFrame.setSize(350,150);

       // define and register window event handler
    mainFrame.addWindowListener(new WindowAdapter()
    {
      public void windowClosing(WindowEvent e) {System.exit(0);}
    });
    
      // create and register the button event handlers
    ConvertButtonHandler chandler = new ConvertButtonHandler();  // instantiate a handler
    convertButton.addActionListener(chandler);  // register the handler    
 
    ExitButtonHandler ehandler = new ExitButtonHandler();  // instantiate a handler
    exitButton.addActionListener(ehandler);  // register the handler    

 
    mainFrame.show();
  } 
  
  
     // inner classes for the button event handlers
  class ConvertButtonHandler implements ActionListener
  {
    public void actionPerformed(ActionEvent e)
    {
      DecimalFormat num = new DecimalFormat(",###.##");
      String instring;      
      double invalue, outvalue;
      
      instring = fahrField.getText();  // read the input value
      invalue = Double.parseDouble(instring);  // convert to a double     
      outvalue = 5.0/9.0 * (invalue - 32.0);     
      celsField.setText(num.format(outvalue));
    }
  }  // end of inner class

  class ExitButtonHandler implements ActionListener
  {
    public void actionPerformed(ActionEvent e)
    {
      System.exit(0);
    }
  }  // end of inner class

  public static void main(String args[])
  {
    new ConvertTempOne();  // instantiate a GUI object 
  }

}  // end of class