7.1 The AdaptingMenu class diagram, data attributes and constructor

The AdaptingMenu class diagram is presented in Figure 7.1.

Figure 7.1 AdaptingMenu class diagram.

The diagram shows that, in addition to the constructor, the class supplies new actions to enable and to disable a menu option; as well as an overloaded offerMenuAsInt action. It also suggests that it provides its own private showMenu action. The implementation of this design as far as the end of the constructor is as follows. 

0001 // Filename Menus/AdaptingMenu.java.
0002 // Providing an extended menu which can change 
0003 // the options which it presents.
0004 //
0005 // Written for JFL book Chapter 7 see text.
0006 // Fintan Culwin, v0.1, January 1997.
0007 
0008 package Menus;
0009 
0010 public class AdaptingMenu extends Menus.BasicMenu { 
0011 
0012 boolean inUse[];
0013 char    optionKey[];
0014 
0015    public AdaptingMenu( String title,
0016                         String options[],
0017                         String prompt) { 
0018                         
0019 
0020       super( title, options, prompt); 
0021       inUse      = new boolean[ options.length]; 
0022       optionKey  = new    char[ options.length]; 
0023    } // End AdaptingMenu constructor.

This class introduces two additional iterative data attributes: a boolean array called inUse which indicates which options are currently in use and a character array called optionKey which indicates which menu key is associated with each option. The use made of these arrays will be described below.

The three arguments of the constructor are used in exactly the same way as the three arguments of the BasicMenu constructor. The first action of the AdaptingMenu constructor is to call the BasicMenu constructor passing on the three arguments. The remaining actions of the constructor are to create the two arrays, inUse and optionKey, with sizes determined by the number of elements in the options argument array. The state of the data attributes of an instance of the AdaptingMenu class, using the same example values as were used for the BasicMenu class immediately after it has been constructed, is shown in Figure 7.2.

Figure 7.2. Default state of the attributes of an AdaptingMenu instance.

The default value of a boolean variable is false and so all values in the inUse array are shown to be false. This will be interpreted to mean that upon construction none of the menu options are active. The default value of a character variable is the null character, shown as ''. The use of the optionKey array will be described below.