Contributed
by
and Tomas Pavek, maintained by Ruth Kusterer and Patrick Keegan
This beginner tutorial teaches you how to create a simple graphical user
interface and add simple back-end functionality. In particular we will show how to code the behavior of
buttons and fields in a Swing form.
We will work through the
layout and design of a GUI and add a few buttons and text field. The text fields
will be used for receiving user input and also for displaying the program output.
The button will initiate the functionality built into the front end.
The application we create will be a simple but functional calculator.
For a more comprehensive guide to the GUI Builder's design features, including video
demonstrations of the various features,
see Designing a Swing GUI in NetBeans IDE.
The first step is to create an IDE project for the application that
we are going to develop. We will name our project NumberAddition.
Choose File > New Project. Alternatively, you can click the New Project
icon in the IDE toolbar.
In the Categories pane, select the Java node. In the Projects pane,
choose Java Application. Click Next.
Type NumberAddition in the Project Name field and specify a path
e.g. in your home directory as the project
location.
Leave the Use Dedicated Folder for Storing Libraries checkbox unselected.
(If you are using NetBeans IDE 6.0, this option is not available.)
Ensure that the Set as Main Project checkbox is selected. Deselect the Create
Main Class checkbox if it is selected.
Click Finish.
Exercise 2: Building the Front End
To proceed with building our interface, we need to create a Java container
within which we will place the other required GUI components. In this step we'll
create a container using the JFrame component. We will place the container
in a new package, which will appear within the Source Packages node.
Create a JFrame container
In the Projects window, right-click the NumberAddition node and choose
New > JFrame Form.
Enter NumberAdditionUI as the class name.
Enter my.numberaddition as the package.
Click Finish.
The IDE creates the NumberAdditionUI form and the
NumberAdditionUI class within the NumberAddition
application, and opens the NumberAdditionUI form in the
GUI Builder. The my.NumberAddition
package replaces the default package.
Adding Components: Making the Front End
Next we will use the Palette to populate our application's front end with a JPanel.
Then we will add three JLabels, three JTextFields, and three JButtons.
If you have not used the GUI Builder before, you might find information in
the GUI Building in NetBeans IDE tutorial
on positioning components useful.
Once you are done dragging and positioning the aforementioned components,
the JFrame should look something like the following screenshot.
If you do not see the
Palette window in the upper right corner of the IDE, choose Windows > Palette.
Start by selecting a JPanel from the Palette and drop it onto the JFrame.
While the JPanel is highlighted, go to the Properties window
and click the ellipsis (...) button next to Border to choose a border style.
In the Border dialog, select TitledBorder from the list,
and type in Number Addition in the Title field.
Click OK to save the changes and exit the dialog.
You should now see an empty titled JFrame that says Number Addition
like in the screenshot. Look at the screenshot and add three
JLabels, three JTextFields and three JButtons as you see above.
Renaming the Components
In this step we are going to rename the display text of the
components that were just added to the JFrame.
Double-click jLabel1 and change the text property to First
Number
Double-click jLabel2 and change the text to Second Number
Double-click jLabel3 and change the text to Result
Delete the sample text from jTextField1. You can make the display text
editable by clicking the
text field, pausing, and then clicking the text field again. You may have to resize the jTextField1 to its original size. Repeat
this step for jTextField2 and jTextField3.
Rename the display text of jButton1 to Clear.
(You can edit a button's text by right-clicking the button and choosing
Edit Text. Or you can click the button, pause, and then click again.)
Rename the display text of jButton2 to Add.
Rename the display text of jButton3 to Exit.
Your Finished GUI should now look like the following screenshot:
Exercise 3: Adding Functionality
In this exercise we are going to give functionality to the Add, Clear, and
Exit buttons. The jTextField1 and jTextField2 boxes will be used for user input
and jTextField3 for program output - what we are creating is a very simple calculator.
Let's begin.
Making the Exit Button Work
In order to give function to the buttons, we have to assign an event
handler to each to respond to events.
In our case we want to know when the button is pressed, either by mouse
click or via keyboard. So we will use ActionListener responding to ActionEvent.
Right click the Exit button.
From the pop-up menu choose Events > Action > ActionPerformed.
Note that the menu contains many more events you can respond to!
When you select the actionPerformed event, the IDE will automatically
add an ActionListener to the Exit button and generate a handler method
for handling the listener's actionPerformed method.
The IDE will open up the Source Code window and scroll to
where you implement the action
you want the button to do when the button is pressed (either by mouse
click or via keyboard).
Your Source Code window should contain the following lines:
We
are now going to add code for what we want the Exit Button to do. You will have to type
System.exit(0); to the above code, replacing the TODO line.
Your finished Exit button code should look like this:
Click the Design tab at the top of your work area to go back to the
Form Design
Right click the Clear button (jButton1). From the pop-up menu select
Events > Action > actionPerformed.
We are going to have the Clear button erase all text from the jTextFields.
To do this, you will add some code like above. Your finished source code should look
like this:
The above code changes the text in all three
of our JTextFields to nothing, in essence it is overwriting the existing
Text with a blank.
Making the Add Button Work
The Add button will perform
three actions.
It is going to accept user input from jTextField1 and jTextField2 and
convert the input from a type String to a float.
It will then perform
addition of the two numbers and finally,
it will convert the sum to a type String
and place it in jTextField3.
Lets get started!
Click the Design tab at the top of your work area to go back to the
Form Design.
Right-click the Add button (jButton3). From the pop-up menu, select Events >
Action > actionPerformed
We are going to add some code to have our Add button work. The
finished source code shall look like this:
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt){
// First we define float variables.
float num1, num2, result;
// We have to parse the text to a type float.
num1 = Float.parseFloat(jTextField1.getText());
num2 = Float.parseFloat(jTextField2.getText());
// Now we can perform the addition.
result = num1+num2;
// We will now pass the value of result to jTextField3.
// At the same time, we are going to
// change the value of result from a float to a string.
jTextField3.setText(String.valueOf(result));
}
Our program is now complete we can now build and run it to see it in action.
Exercise 4: Running the Program
The final step is to build and run the program.
Choose Build > Build Main Project.
When the Build output is finished,
choose Run > Run Main Project
If you get a window informing you
that Project NumberAddition does not have a main class set, then
you should select my.NumberAddition.NumberAdditionUI as the main
class in the same window and click the OK button.
Your created program is now running.
In this tutorial you learned how you hook up functionality to
GUI components with the NetBeans GUI Builder.
How Event Handling Works
This tutorial showed how to respond to a simple button event.
There are many more events you can have your application respond to. The IDE can help you find the
list of available events your GUI components can handle:
Go back to the file NumberAdditionUI.java in the Editor.
Click the Design tab to see the GUI's layout in the GUI Builder.
Right-click any GUI component, and select Events from the pop-up menu.
For now, just browse the menu to see what's there, you don't need to select anything.
Alternatively, you can select Properties from the Window menu. In the Properties window, click the Events tab.
In the Events tab, you can view and edit events handlers associated with the currently active GUI component.
You can have your application respond to key presses, single,
double and triple mouse clicks, mouse motion, window size and focus changes.
You can generate event handlers for all of them from the Events menu.
The most common event you will use is an Action event.
(Learn best practices for Event handling from Sun's Java Events Tutorial.)
How does event handling work? Everytime you select an event from the Event menu,
the IDE automatically creates a so-called event listener for you, and hooks it up to your component.
Go through the following steps to see how event handling works.
Go back to the file NumberAdditionUI.java in the Editor. Click the Source tab to see the GUI's source.
Scroll down and note the methods jButton1ActionPerformed(),
jButton2ActionPerformed(), and jButton3ActionPerformed() that you just implemented.
These methods are called event handlers.
Now scroll to a method called initComponents(). If you do not see this method,
look for a line that says Generated Code; click the + sign next to it
to expand the collapsed initComponents() method.
First, note the blue block around the initComponents() method. This code was auto-generated
by the IDE and you cannot edit it.
Now, browse through the initComponents() method. Among other things,
it contains the code that initializes and places your GUI components on the form.
This code is generated and updated automatically while you place and edit components in the Design view.
This is the spot where an event listener object is added to the GUI component;
in this case, you register an ActionListener to the jButton3.
The ActionListener interface has an actionPerformed method taking ActionEvent
object which is implemented simply by calling your jButton3ActionPerformed event handler.
The button is now listening to action events. Everytime it is pressed an
ActionEvent is generated and passed to the listener's actionPerformed method
which in turn executes code that you provided in the event handler for this event.
Generally speaking, to be able to respond, each interactive GUI component
needs to register to an event listener and needs to implement an event handler.
As you can see, NetBeans IDE handles hooking up the event listener for you, so you can concentrate
on implementing the actual business logic that should be triggered by the event.
If you have questions or need support,
and want to keep yourself informed on the latest
developments on the NetBeans IDE features,
join the
mailing list by
sending an empty message to
.
