The main form for the application is shown in the following Form Designer image:

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Kerry Martin
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The main form for the application is shown in the following Form Designer image: You can see that there are two text fields (txtnumofnums and txthighest) that are used to capture the parameters of

1 Horstmann & Cornell Example 3-7 Page 1 This example demonstrates the use of methods that are not associated with specific events. In addition to the requirements given in the text, the example also demonstrates the use of a dialog box to display the results. The main form for the application is shown in the following Form Designer image: You can see that there are two text fields (txtnumofnums and txthighest) that are used to capture the parameters of the problem. There is also a JButton used by the user to compute the odds. The code for this main form (the JFrame1 class) includes a method called lotteryodds as described in class. This code may be entered anywhere within the class definition but not within another method. I added the code right before the closing } for the class. The code window follows:

Horstmann & Cornell Example 3-7 Page 2 You will notice that there is one significant difference between this code and the version shown in the text.

I disagree with the authors in their decision to use a method like this as an example of a class method.

2 Horstmann & Cornell Example 3-7 Page 2 You will notice that there is one significant difference between this code and the version shown in the text. This code is not a class method, but instead it is a private instance method. That is, instead of starting with public static, it starts with private and does not include the word static. I disagree with the authors in their decision to use a method like this as an example of a class method. Class methods are typically called from other classes without having to create an object of that class. For example, we have used the Math.pow() method several times. The pow() method is a class method in the Math class. We used it simply by referring to it not by first creating an object from the Math class. Our method is going to be used internally by our class (JFrame1) and therefore I do not think it makes sense to make it a class method. The JButton s actionperformed event is very similar to the one in the text except for its use of a dialog box to display the results. The code for this event is: The last four lines of code need some explanation. The first line creates (instantiates) a new object reference oddsdialog that points to a JDialog1 object. We ll see where the definition for the JDialog1 came from later. The second line passes the computed odds to the dialog object so that it has the information to display to the user. The third line causes the dialog object to be set as a modal dialog. This means that the user must close this dialog before control returns to the method that caused the dialog box to be displayed. The final statement causes the dialog box to be displayed. That actual dialog box is shown below.

You will see a new Form Designer window with a JDialog component just like the previous examples with a JFrame component.

3 Horstmann & Cornell Example 3-7 Page 3 How do we create the dialog class and add it to our project? Start by selecting the Project Window. With this window as the active window, select Form from the Insert menu. From the ensuing Insert Form dialog box, select JDialog. You will see a new Form Designer window with a JDialog component just like the previous examples with a JFrame component. You can add components from the toolbox to this window just like you ve done with JFrames. The Form Designer for this dialog is shown below: The dialog box includes one JLabel (named lblodds) and a JButton (cmdclose). The JButton s Text property has been set to Close and its Mnemonic property has been set to C. The Mnemonic property is used to create an access key (note that the C is underlined). A private variable (called an instance variable) named fodds has been added to the JDialog1 class. It has been located before the first (constructor) method of the class. The first few lines of code are:

4 Horstmann & Cornell Example 3-7 Page 4 This instance variable stores the odds computed in the JFrame1 class. Recall that in the actionperformed event for the JButton in the JFrame1 class there was the following statement: oddsdialog.setodds(odds); This statement calls the setodds method (called an accessor method). We need to add this method to the JDialog1 code. The code for the method is shown below: Just like the lotteryodds method in the JFrame1 class, this method is added at the end of the code right before the JDialog1 class s closing }. This public method accepts a long-type parameter and stores it in the instance variable fodds. When the dialog box is shown, its windowopened event is called. We use this event to construct a string and place it in the JLabel (lblodds) in JDialog1 (see below). Remember that if you are going to refer to the NumberFormat class, you need to import the java.text.* package. Look back to the screen image that showed the declaration of the fodds instance variable and you will see the import statement that has been added. Be aware that importing a package into a class only applies to that class (and any descendents). In particular, if you placed the import statement in the code for the JFrame1 class, not the JDialog1 class, then an error would have occurred.

Horstmann & Cornell Example 3-7 Page 5 Finally, when the user clicks on the Close button, its actionperformed event is called. The code for this event is: The statement this.

5 Horstmann & Cornell Example 3-7 Page 5 Finally, when the user clicks on the Close button, its actionperformed event is called. The code for this event is: The statement this.setvisible(false); causes the dialog box to no longer be visible. You might wonder what the word this means in the code. In a method, the keyword this refers to the object on which the method operates. Since the actionperformed method is part of the JDilaog1 class, the keyword this refers to this JDialog1 object. Thus it caused the dialog box to no longer be visible.

Encapsulation. Administrative Stuff. September 12, Writing Classes. Quick review of last lecture. Classes. Classes and Objects

Encapsulation. Administrative Stuff. September 12, Writing Classes. Quick review of last lecture. Classes. Classes and Objects Administrative Stuff September 12, 2007 HW3 is due on Friday No new HW will be out this week Next Tuesday we will have Midterm 1: Sep 18 @ 6:30 7:45pm. Location: Curtiss Hall 127 (classroom) On Monday