//
// Description:
// 1) User types an integer into input text field
// 2) User presses "convert" button.
// 3) Program parses input integer, switches the sign, and displays
//    the converted integer in the output text field.
//
// INPUT: integer typed in textfield
// Warning: there is no error checking on this field, input must be 
//          valid integer.
//
// OUTPUT: an integer with the opposite sign of the input integer
// is displayed in the output text field.
//
// NOTES:
// - This is the first program where we see a "listener".
//   This is necessary to respond to button presses; we will cover
//   listeners in much more detail soon. 
//=================================================================

import java.awt.*;
import java.applet.*;
import java.awt.event.*;           // Necessary for listener to respond
				   // to button press 

public class SwitchSign extends Applet implements ActionListener
{
   private Button      convertButton;     // button to cause action
   private TextField   inputDisplay;      // type input integer here
   private TextField   outputDisplay;     // display converted int here
   
   //------------------------------------------------------------------
   // init()
   // Create widgets and add them to the applet.
   // Register an action listener with the convert button.
   //------------------------------------------------------------------
   public void init ()
   {
      Label inputLabel = new Label("Enter Input Integer Here:");
      Label outputLabel =  new Label("Converted Integer Here:");
      Panel p1 = new Panel();
      Panel p2 = new Panel();
      Panel p3 = new Panel();
      
      // We put the buttons and textFields into separate panels so
      // that when we use the GridLayout these items stay "regular"
      // size instead of expanding to fill the space.
      
      // Create a new "convert" button.  Add the action listener to
      // respond to button presses.
      convertButton = new Button("Convert");
      convertButton.addActionListener(this);
      p3.add(convertButton);
      
      inputDisplay = new TextField(10);
      p1.add(inputDisplay);
      
      outputDisplay = new TextField(10);
      p2.add(outputDisplay);
      outputDisplay.setEditable(false);
      
      setLayout(new GridLayout(3,2));
      add(inputLabel);
      add(p1);
      add(outputLabel);
      add(p2);
      add(p3);
   }  // end init method
      
   //------------------------------------------------------------------
   // actionPerformed
   // Respond to button presses by:
   // 1) Scanning the input integer from the input text field
   // 2) Converting the input integer by multiplying with -1
   // 3) Displaying the new integer in the output text field
   //------------------------------------------------------------------
   public void actionPerformed ( ActionEvent e )
   {
      String input;
      String command;
      int    number;

      // Not really necessary since there is only one button.
      // This would be important if there were more than one button
      // to distinguish the different commands of each button.
      
      command = e.getActionCommand();
      
      if ( command.equals("Convert") )
      {
	 input = inputDisplay.getText();
	 number = Integer.parseInt(input);
	 number = number * -1;
	 outputDisplay.setText(Integer.toString(number));
      }
      
   } // end actionPerformed method
   
}  // end SwitchSign class