Learning Swing with the NetBeans IDE

Learning Swing with the NetBeans IDE

NetBeans IDE Basics

It is not necessary to learn every feature of the NetBeans IDE before exploring its GUI creation capabilities. In fact, the only features that you really need to understand are the Palette, the Design Area, the Property Editor, and the Inspector. We will discuss these features below.

The Palette                             

The Palette contains all of the components offered by the Swing API. You can probably already guess what many of these components are for, even if this is your first time using them (JLabel is a text label, JList is a drop-down list, etc.)

From this list, our application will use only JLabel (a basic text label), JTextField (for the user to enter the temperature), and JButton (to convert the temperature from Celsius to Fahrenheit.)

The Design Area

The Design Area is where you will visually construct your GUI. It has two views: source view, and design view. Design view is the default, as shown below. You can toggle between views at any time by clicking their respective tabs.

The figure above shows a single JFrame object, as represented by the large shaded rectangle with blue border. Commonly expected behavior (such as quitting when the user clicks the "close" button) is auto-generated by the IDE and appears in the source view between uneditable blue sections of code known as guarded blocks.

The Property Editor

The Property Editor does what its name implies: it allows you to edit the properties of each component. The Property Editor is intuitive to use; in it you will see a series of rows — one row per property — that you can click and edit without entering the source code directly. The following figure shows the Property Editor for the newly added JFrame object:

The screenshot above shows the various properties of this object, such as background color, foreground color, font, and cursor.

The Inspector

The last component of the NetBeans IDE that we will use in this lesson is the Inspector:

The Inspector provides a graphical representation of your application's components.

Creating the Celsius Converter in  GUI

The goal of this section is to introduce the Swing API by designing a simple application that converts temperature from Celsius to Fahrenheit. Its GUI will be basic, focusing on only a subset of the available Swing components.

the following steps describe settings that are specific to this application, so take care to follow them closely.

Step 1: Create a New Project

To create a new project, launch the NetBeans IDE and choose New Project from the File menu:

Step 2: Choose General -> Java Application

Next, select General from the Categories column, and Java Application from the Projects column:

You may notice mention of "J2SE" in the description pane; that is the old name for what is now known as the "Java SE" platform. Press the button labeled "Next" to proceed.

Step 3: Set a Project Name

Now enter "CelsiusConverterProject" as the project name. You can leave the Project Location and Project Folder fields set to their default values, or click the Browse button to choose an alternate location on your system.

Make sure to deselect the "Create Main Class" checkbox; leaving this option selected generates a new class as the main entry point for the application, but our main GUI window (created in the next step) will serve that purpose, so checking this box is not necessary. Click the "Finish" button when you are done.

When the IDE finishes loading, you will see a screen similar to the above. All panes will be empty except for the Projects pane in the upper left hand corner, which shows the newly created project.

Step 4: Add a JFrame Form

Now right-click the CelsiusConverterProject name and choose New -> JFrame Form (JFrame is the Swing class responsible for the main frame for your application.) You will learn how to designate this class as the application's entry point later in this lesson.

Step 5: Name the GUI Class

Next, type Celsius Converter GUI as the class name, and learn as the package name. You can actually name this package anything you want, but here we are following the tutorial convention of naming the package after the lesson in which is resides.

The remainder of the fields should automatically be filled in, as shown above. Click the Finish button when you are done.

When the IDE finishes loading, the right pane will display a design-time, graphical view of the Celsius Converter GUI. It is on this screen that you will visually drag, drop, and manipulate the various Swing components.

Step 1: Set the Title

First, set the title of the application's JFrame to "Celsius Converter", by single-clicking the JFrame in the Inspector:

Then, set its title with the Property Editor:

You can set the title by either double-clicking the title property and entering the new text directly, or by clicking the dot button and entering the title in the provided field. Or, as a shortcut, you could single-click the JFrame of the inspector and enter its new text directly without using the property editor.

Step 2: Add a JTextField

Next, drag a JTextField from the Palette to the upper left corner of the Design Area. As you approach the upper left corner, the GUI builder provides visual cues (dashed lines) that suggest the appropriate spacing. Using these cues as a guide, drop a JTextField into the upper left hand corner of the window as shown below:

Step 3: Add a JLabel

Next, drag a JLabel onto the Design Area. Place it to the right of the JTextField, again watching for visual cues that suggest an appropriate amount of spacing. Make sure that text base for this component is aligned with that of the JTextField. The visual cues provided by the IDE should make this easy to determine.

Step 4: Add a JButton

Next, drag a JButton from the Palette and position it to the left and underneath the JTextField. Again, the visual cues help guide it into place.

Step 5: Add a Second JLabel

Adding a Second JLabel

Finally, add a second JLabel, repeating the process in step 2. Place this second label to the right of the JButton, as shown above.

Step 6: Set the Component Text

First,double-click the jTextField and JButton to change the default text that was inserted by the IDE. When you erase the text from the JTextField, it will shrink in size as shown below. Change the text of the JButton from "JButton1" to "Convert." Also change the top JLabel text to "Celsius" and the bottom to "Fahrenheit."

Setting the Component Text

Step 7: Set the Component Size

Next,shift-click the jTextField and JButton components. This will highlight each showing that they are selected. Right-click (control-click for mac users) Same Size -> Same Width. The components will now be the same width, as shown below. When you perform this step, make sure that JFrame itself is not also selected. If it is, the Same Size menu will not be active.

Setting the JTextField and JButton Sizes

Step 8: Remove Extra Space

Finally, grab the lower right-hand corner of the JFrame and adjust its size to eliminate any extra whitespace. Note that if you eliminate all of the extra space (as shown below) the title (which only appears at runtime) may not show completely. The end-user is free to resize the application as desired, but you may want to leave some extra space on the right side to make sure that everything fits correctly. Experiment, and use the screenshot of the finished GUI as a guide.

The Completed GUI

The GUI portion of this application is now complete! If the NetBeans IDE has done its job, you should feel that creating this GUI was a simple, if not trivial, task. But take a minute to click on the source tab; you might be surprised at the amount of code that has been generated.

To see the code in its entirety, scroll up and down within the IDE as necessary. You can expand or collapse certain blocks of code (such as method bodies) by clicking the + or - symbol on the left-hand side of the source editor

Step 9: Change the Default Variable Names

The figure below shows the default variable names as they currently appear within the Inspector. For each component, the variable name appears first, followed by the object's type in square brackets. For example, jTextField1 [JTextField] means that "jTextField1" is the variable name and "JTextField" is its type.

Default Variable Names

The default names are not very relevant in the context of this application, so it makes sense to change them from their defaults to something that is more meaningful. Right-click each variable name and choose "Change variable name." When you are finished, the variable names should appear as follows:

New Variable Names

The new variable names are "tempTextField", "celsiusLabel", "convertButton", and "fahrenheitLabel." Each change that you make in the Inspector will automatically propagate its way back into the source code. You can rest assured that compilation will not fail due to typos or mistakes of that nature — mistakes that are common when editing by hand.

Step 10: Register the Event Listeners

When an end-user interacts with a Swing GUI component (such as clicking the Convert button), that component will generate a special kind of object — called an event object — which it will then broadcast to any other objects that have previously registered themselves as listeners for that event. The NetBeans IDE makes event listener registration extremely simple:

In the Design Area, click on the Convert button to select it. Make sure that only the Convert button is selected (if the JFrame itself is also selected, this step will not work.) Right-click the Convert button and choose Events -> Action -> ActionPerformed. This will generate the required event-handling code, leaving you with empty method bodies in which to add your own functionality:

There are many different event types representing the various kinds of actions that an end-user can take (clicking the mouse triggers one type of event, typing at the keyboard triggers another, moving the mouse yet another, and so on.) Our application is only concerned with the ActionEvent; for more information about event handling,

Step 11: Add the Temperature Conversion Code

The final step is to simply paste the temperature conversion code into the empty method body. The following code is all that is necessary to convert a temperature from Celsius to Fahrenheit:

    //Parse degrees Celsius as a double and convert to Fahrenheit.

    int tempFahr = (int)((Double.parseDouble(tempTextField.getText()))

            * 1.8 + 32);

    fahrenheitLabel.setText(tempFahr + " Fahrenheit");

Simply copy this code and paste it into the convertButtonActionPerformed method as shown below:

With the conversion code in place, the application is now complete.

Step 12: Run the Application

Running the application is simply a matter of choosing Run -> Run Main Project within the NetBeans IDE. The first time you run this application, you will be prompted with a dialog asking to set CelsiusConverterGUI as the main class for this project. Click the OK button, and when the program finishes compiling, you should see the application running in its own window.

Congratulations! You have completed your first Swing application!