// Demo 17: MartianTranslatorApplet.java

//   A Martian To English and English To Martian Translator
//                 A Java Applet
//
//            by Charles W. Neville, 1998
//         Copyright Charles W. Neville, 1998

// Those of you who remember the Trix Rabbit will remember the cereal box where 
// he went to Mars.  All the kids (the Martian kids in this case) got Trix, but 
// the poor Trix Rabbit didn't get any at all, because, as usual, "Silly 
// Rabbit, Trix are for kids!"  This was most unfair to our hero because 
// he made a great discovery on his trip to Mars: The Martian language is 
// simply English spelled backwards!  Personally, I feel NASA should reward our 
// intrepid and learned Rabbit for his great discovery by immediately providing 
// him with a bowl of Trix.  But in the meantime, we can exploit his discovery 
// by writing a Martian to English and English to Martian translator.

// The idea behind our Martian to English translator is simple:  Convert a 
// String entered by the user in a TextField to an ARRAY of chars.  Then copy 
// the array of chars BACKWARDS to another array of chars, and convert it back 
// to a String.  Finally, draw the string on the applet panel.

// Note that because reversing a string twice gives you (a copy of) the 
// original string back, our translator works both ways: You can translate from 
// English to Martian as easily as you can translate from Martian to English. 
// Also, our translator gives us valuable practice with arrays and Strings.
// The key work is done in the translate method.  Finally, just to dress up the
// user interface, we get an introduction to another AWT component, namely
// Buttons, and we get an introduction to multiple event handling in the 
// actionPerformed method using the getActionCommand() method of an ActionEvent
// object.

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;

public class MartianToEnglishApplet extends Applet implements ActionListener {

   // User interface variables
   Label inputPrompt;     // prompt on Applet Panel for TextField input
   TextField inputField;  // where we enter either Martian or English 
                          // sentences.
   String outputPrompt;   // where we say whether output is in Martian
                          // or English
   Button martianButton;  // press to translate from Martian to English
   Button englishButton;  // press to translate from English to Martian

   // Translator variables
   char[ ] inputChars;  // char array holding input characters
   char[ ] outputChars;  // char array holding output (translated) characters
   String inputString; // String holding input string
   String outputString; // String holding output (translated) string


   // build Applet panel and initialize, as usual.
   public void init() {

      // create new instances of labels, textfields and buttons
      inputPrompt = new Label("Martian: ");
      inputField = new TextField(50);  // 50 characters possible input
      englishButton = new Button("English");
      martianButton = new Button("Martian");

     // add components to Applet Panel
     add(inputPrompt);
     add(inputField);
     add(martianButton);
     add(englishButton);

     // Register TextField and Buttons as the ActionListeners
     // (ActionEvent processors) for this Applet
     inputField.addActionListener(this);
     martianButton.addActionListener(this);
     englishButton.addActionListener(this);

     outputPrompt = "English: ";  // default is Martian to English translation
     outputString = "";
   }

   // translate from Martian to English, or vice versa
   public void translate() {

       inputString = inputField.getText(); // get user's input string
       inputChars = inputString.toCharArray(); // convert to char array

       outputChars = new char[inputChars.length]; // create array

       // outputChars is inputChars backwards
       for(int i = 0; i < inputChars.length; i++) {

          outputChars[inputChars.length - 1 - i] = inputChars[i];
       }

       outputString = String.valueOf(outputChars);
   }

   public void paint(Graphics g) {

      g.drawString(outputPrompt + outputString, 25, 100);

   }

   public void actionPerformed(ActionEvent e) {

      // method getActionCommand() returns the String value of the
      // ActionEvent e.  In the case of a Button click, it returns the
      // the title string on the Button.

      // when comparing two strings for content equality, 
      // ALWAYS use method equals NEVER use ==
      if( e.getActionCommand().equals("Martian") ) {

        inputPrompt.setText("Martian: ");  // set text string on label
                                         // to "Martian"

        outputPrompt = "English: ";  // we will draw "English" on Applet panel
      }
      else if( e.getActionCommand().equals("English") ){

        inputPrompt.setText("English: ");  // set text string on label
                                         // to "English"

        outputPrompt = "Martian: ";  // we will draw "Martian" on Applet panel
      }
      else { // we pressed Enter key while in input text field

         translate();
      }

      repaint();
    }
}