A Demo is Worth a Thousand Words

With BreezyGUI

import java.awt.*;
import BreezyGUI.*;

public class TemperatureConversion extends GBFrame {

   private Label fahrenheitLabel         
                        = addLabel  ("Degrees Fahrenheit",1,1,1,1);
   private Label centigradeLabel        
                        = addLabel  ("Degrees Centigrade",2,1,1,1);
   private IntegerField fahrenheitField 
                        = addIntegerField (32            ,1,2,1,1);
   private IntegerField centigradeField 
                        = addIntegerField (0             ,2,2,1,1);
   private Button fahrenheitButton      
                        = addButton ("Compute Fahrenheit",3,1,1,1);
   private Button centigradeButton      
                        = addButton ("Compute Centigrade",3,2,1,1);

   public void buttonClicked (Button buttonObj){
      int fahrenheit, centigrade;
      if (buttonObj == fahrenheitButton){
         centigrade = centigradeField.getNumber();
         fahrenheit = centigrade * 9 / 5 + 32;
         fahrenheitField.setNumber (fahrenheit);
      }else{
         fahrenheit = fahrenheitField.getNumber(); 
         centigrade = (fahrenheit  - 32) * 5 / 9;
         centigradeField.setNumber (centigrade);
      }
   }

   public static void main (String[] args){
      Frame frm = new TemperatureConversion ();
      frm.setSize (200, 150);
      frm.setVisible (true);
   }
}

Without BreezyGUI

import java.awt.*;

public class ConversionWithAWT extends Frame {
    
   private Label     fahrenheitLabel;
   private TextField fahrenheitField;
   private Label     centigradeLabel;
   private TextField centigradeField;
   private Button    fahrenheitButton;
   private Button    centigradeButton;

   public ConversionWithAWT(){
        
      fahrenheitLabel  = new Label ("Degrees Fahrenheit");
      fahrenheitField  = new TextField ("212", 6);  // 6 columns wide
      centigradeLabel  = new Label ("Degrees Centigrade");
      centigradeField  = new TextField ("100", 6);  // 6 columns wide
      fahrenheitButton = new Button ("Compute Fahrenheit");
      centigradeButton = new Button ("Compute Centigrade");
              
      FlowLayout layout = new FlowLayout();
      setLayout (layout);
        
      add (fahrenheitLabel);
      add (fahrenheitField);
      add (centigradeLabel);
      add (centigradeField);
      add (fahrenheitButton);
      add (centigradeButton);
            
      fahrenheitButton.addActionListener 
                                 (new FahrenheitButtonListener (this));
      centigradeButton.addActionListener 
                                 (new CentigradeButtonListener (this));
  
      fahrenheitField.addKeyListener (new DigitKeyListener());
      centigradeField.addKeyListener (new DigitKeyListener());

      addWindowListener (new GenericWindowListener());
   }
   
   public void computeFahrenheit(){
      String str = centigradeField.getText().trim();
      int centigrade = (new Integer (str)).intValue();
      int fahrenheit = centigrade * 9 / 5 + 32;
      fahrenheitField.setText ("" + fahrenheit);
   }

   public void computeCentigrade(){
      String str = fahrenheitField.getText().trim();
      int fahrenheit = (new Integer (str)).intValue();
      int centigrade = (fahrenheit - 32) * 5 / 9;  
      centigradeField.setText ("" + centigrade);
   }

   public static void main (String[] args){
      Frame frm = new ConversionWithAWT();
      frm.setSize (250, 150);
      frm.setVisible (true);
   }
}

=======================================

import java.awt.event.*;

public class CentigradeButtonListener implements ActionListener{
   
   private ConversionWithAWT theGUI;

   public CentigradeButtonListener (ConversionWithAWT gui){
      theGUI = gui;
   }   

   public void actionPerformed (ActionEvent e){
      theGUI.computeCentigrade();
   }
}

=======================================

import java.awt.event.*;

public class FahrenheitButtonListener implements ActionListener{

   private ConversionWithAWT theGUI;

   public FahrenheitButtonListener (ConversionWithAWT gui){
      theGUI = gui;
   }   

   public void actionPerformed (ActionEvent e){
      theGUI.computeFahrenheit();
   }
}

=======================================

import java.awt.event.*;

public class DigitKeyListener extends KeyAdapter{

   public void keyTyped(KeyEvent e){
      char ch = e.getKeyChar();
      if (! Character.isDigit(ch))
         e.consume();
   }

}

=======================================

import java.awt.event.*;

public class GenericWindowListener implements WindowListener{

   public void windowClosing (WindowEvent e){
      System.exit(0);
   }
   
   public void windowActivated (WindowEvent e){}
   public void windowClosed (WindowEvent e){}
   public void windowDeactivated (WindowEvent e){}
   public void windowDeiconified (WindowEvent e){}
   public void windowIconified (WindowEvent e){}
   public void windowOpened (WindowEvent e){}
}