/** Program 6.6 Applet that Checks for Balanced Parentheses */
/*
 * This applet accepts a string typed by the user that contains parentheses
 * in the set '{','(','[','}',')',']' and checks it for parenthesis balance
 */
import java.applet.*;
import java.awt.*;

public class ParenMatchApplet extends Applet implements ActionListener {
// declare the data fields as follows:
   Label
      instructionLabel,   // gives the instructions for user input
      inputLabel,                     // labels the input text box
      outputLabel;                   // labels the output text box
   TextField
      inputField,                            // the input text box
      outputField;                          // the output text box

   ParenMatcher PM;            // the object that computes results

   // the applet's methods follow

   /*----------------------------------------*/

   public void init() {
  
      instructionLabel = new Label(
         "Type an input expression in the box below, and press the Enter key.",
         Label.CENTER);

      add(instructionLabel);       // add the instruction label to
                                           // top of applet layout
      inputLabel = new Label(" input:");
     
      add(inputLabel);                // then, add the input label
     
      inputField = new TextField(40);   // create a 40-column-wide
                                      // input field and add it to
      add(inputField);                      // the applet's layout

      inputField.addActionListener(this); // add the event handler
     
      outputLabel = new Label("output:");  // add the output label
     
      add(outputLabel);
     
      outputField = new TextField(40);  // create a 40-column-wide
                                     // output field and add it to
      add(outputField);                     // the applet's layout
        
      inputField.requestFocus(); // put the blinking vertical text
                              // insertion cursor in the input box
      PM = new ParenMatcher();                     // create a new
                                     // parenthesis matcher object
   } // end init

   /*----------------------------------------*/
   
   public void actionPerformed(ActionEvent e)  {
   
      PM.setInput(e.getActionCommand());// send the input string to the
                                      // parenthsis matcher object, PM.
      PM.parenMatch();                   // analyze parenthesis balance
   
      outputField.setText(PM.getOutput());// put result in output field
 
   } // end actionPerformed
  
   /*----------------------------------------*/
   
}// end applet