Creating Menus and Button Arrays Using the Abstract Windows Toolkit - Java Programming: Comprehensive Concepts and Techniques - page 408

To Enter Code for the Numeric and Decimal Point Button Clicks

1. Enter lines 176 through 196 as shown in Figure 6-28 on page 406.
The TextPad window displays the code to test for button clicks of the
numeric buttons or the decimal point button (Figure 6-29). When executed,
the array will be searched, and the switch structure will look for numeric
buttons and the decimal point. When found, the labels from the buttons will
display in the lcd TextField, concatenated with previously displayed labels as
needed.

for loop to
search array until
key is found

flag set to false

if statement to find which
button was clicked

switch header

multiple case
statements

if flag is
set to true

sets button label to
display in lcd TextField

FIGURE 6-29

concatenates multiple
numbers if needed

The boolean flag, foundKey, allows the program to exit the loop if a match is
found in line 184, thereby saving time and making the program more efficient.

Searching for the First Operator Button Click

Figure 6-30 displays the code to search the array and add functionality to
the operator buttons within the actionPerformed() method. Line 198 displays
the case statements that correspond to the operator buttons in the keys. If any of
the cases occur, meaning that the user clicked one of the buttons between 10
through 14, execution of the code passes to the first non-case statement, which is
seen in line 199.

197 // operator buttons

198 case 10: case 11: case 12: case 13: case 14:

199 clearText = true ;

200
201

if ( first ) // first operand

202 {

203 if ( lcd.getText () .length () ==0 ) op1 = 0.0;

204 else op1 = Double .parseDouble ( lcd.getText ()) ;

205
206

first = false ;

207 clearText = true ;

208 lastOp = i; // save last operator

209 }

FIGURE 6-30