The BasicPump design

The TextMenuTuttleInterface class supplies the part of the interface shown at the bottom of Figure 7.2, consisting of a single non-editable TextArea instance. The implementation of this class, as far as the end of its constructor, is as follows.

0001  // Filename TextMenuTuttleInterface.java. 0002  // Supplies text menu interface for a Tuttle. 0003  // 0004  // Written for Java Interface book chapter 7. 0005  // Fintan Culwin, v 0.2, August 1997. 0006   0007  package TextMenuTuttle; 0008   0009  import java.awt.*; 0010  import java.applet.*; 0011  import java.awt.event.*; 0012   0013   0014  class TextMenuTuttleInterface extends Panel {    0015   0016  protected static final int TOP_LEVEL_MENU        = 0; 0017  protected static final int MOVE_MENU             = 1;  0018  protected static final int MOVE_FORWARD_MENU     = 2;  0019  protected static final int MOVE_BACKWARD_MENU    = 3;  0020  protected static final int TURN_MENU             = 4;  0021  protected static final int TURN_LEFT_MENU        = 5; 0022  protected static final int TURN_RIGHT_MENU       = 6;   0023  protected static final int COLOR_MENU            = 7; 0024  protected static final int FOREGROUND_COLOR_MENU = 8; 0025  protected static final int BACKGROUND_COLOR_MENU = 9; 0026  protected static final int PEN_MENU              = 10; 0027  protected static final int SCREEN_MENU           = 11; 0028  protected static final int HELP_MENU             = 12; 0029  protected static final int EXIT_MENU             = 13; 0030   0031  private int                menuState             = TOP_LEVEL_MENU; 0032   0033  private TextArea menuArea; 0034   0035     protected TextMenuTuttleInterface( KeyListener itsListener) {  0036                                0037        menuArea  = new TextArea( 5, 60); 0038        menuArea.setEditable( false); 0039        menuArea.addKeyListener( itsListener); 0040          0041        this.add( menuArea);       0042     } // End TextMenuTuttleInterface constructor.   

The class declaration, on line 0014, indicates that it extends the Panel class. It commences, on lines 0016 to 0029, with the declaration of fourteen protected manifest values to represent the possible states of the interface and, on line 0031, an instance attribute called menuState to record the state of the menu. The intention is that the menuState attribute will always reflect the menu which the interface is currently showing. Two protected methods, setMenuState() and menuStateIs() are provided to support the use of this attribute. As these resources are protected they can be seen by the only other class in the package, the textMenuTuttle class, nut are invisible outside the package. The use which the textMenuTuttle class makes of this knowledge will be described below.

The constructor, on lines 0035 to 0042, creates a non-editable TextArea instance, called menuArea, with 5 rows and 60 columns, and registers the KeyListener instance, itsListener, passed as an argument as its KeyListener attribute. This will cause the appropriate methods in itsListener to be called as the user operates the keyboard. The constructor concludes by adding the menuArea instance into itself as its only instance child. The implementation of the setMenuState() method is as follows.

0046     protected void setMenuState( int newState) {  0047   0048        menuState = newState; 0049         0050        switch( menuState) {  0051           case TOP_LEVEL_MENU: 0052              menuArea.setText( topLevelMenu); 0053              break; 0054               0055           case MOVE_MENU:              0056              menuArea.setText( topLevelMenu + moveMenu);                     0057              break; 0058               0059           case MOVE_FORWARD_MENU:              0060              menuArea.setText( topLevelMenu + moveMenu + movefMenu);                                0061              break; ----           // Other cases omitted. 0103           case EXIT_MENU:       0104              menuArea.setText( topLevelMenu + exitMenu);                                            0105              break;                                    0106           } // End switch.             0107     } // End setMenuState.

The method commences, on line 0048, by setting the value of menuState to the value of the argument passed to the method in newState. It continues with a multi-way switch structure containing a branch for each possible menu state and, within each branch, calls the menuArea's setText() method to cause the appropriate menu to be shown to the user. To accomplish this a number of Strings are declared at the end of the class, for example the Strings referred to in the fragment above are declared as follows.

0115  private static final String topLevelMenu       =   0116                 "  Move Turn Colors Pen Screen Help Exit"; 0117  private static final String moveMenu       =   0118                 "\n    Move: Forwards Backwards"; 0119  private static final String movefMenu      =   0120                 "\n        Move Forwards: 5 10 25 "; ----           // Other cases omitted. 0141  private static final String exitMenu       =   0142                 "\n    Exit: Yes No";                                                              0143  } // End class TextMenuTuttleInterface.

Thus on line 0060 as the interface moves into the MOVE_FORWARD_MENU state, the three strings on lines 0116, 0118 and 0120 are catenated together and displayed in the menuArea to produce the appearance shown in the lower illustration from Figure 7.3. The only other method of this class is the inquiry method menuStateIs(), whose implementation is as follows.

0110     protected int menuStateIs() {     0111        return menuState;    0112     } // End menuStateIs.

 

---

TextMenuTuttleInterface.java

---

7.4 The TextMenuTuttle class

7.2 The TextMenuTuttle interface

---