Swing Button and Text Area Function

Hello everybody,

I started learning Java two months ago and started Swing today :)

After several attempts on how to give a button a function, I succeeded:

Code:

---

JButton generate = new JButton("Generate");
                generate.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent ev) {
                   
                }
                });

---

Now, my doubt is how to change the text of a text area when pressing a button.

So, for example:

The user opens the program and the text "HELLO DUDE 1" is written in a text area. When the button is clicked the text of a textArea will be changed to "YOU PRESSED THIS BUTTON". How can I do it? In C# this would be very easy but I'm new to Java GUI and to Java-Forums.org as well :)

Thanks in advance,

ScoutDavid

Once you pressed the button, you will call the actionPerformed method, do in it whatever you want...

Code:

---

public void actionPerformed(ActionEvent ev) {
        // catch your JTextArea in the variable textArea
        textArea.setText("Whatever you want");
    }

---

Code:

---

Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: Uncompilable source code - local variable TextArea is accessed from within inner class; needs to be declared final
        at javagui.Main$1.actionPerformed(Main.java:24)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6267)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6032)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2478)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

---

I tried that and got this :(

Learn reading the console output, the solution is in the very first line of your error...

Code:

---

Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: Uncompilable source code - local variable TextArea is accessed from within inner class; needs to be declared final

---

Yes, of course, I do understand what I need to do (theorically):

Code:

---

public void actionPerformed(ActionEvent ev) {
                    TextArea.setText("Hello");
                }

---

This is my code and I use TextArea which is defined outside the function, inside the function. This can't be done but it's what I need to do :s Any ideas?

"local variable TextArea is accessed from within inner class; needs to be declared final"

Note that when you access a local variable from within an inner class, you need to declare it as final to refer to the same object during its lifetime.

Also, rename your variable so that the first letter is never a capital. Else it is seen as a Class Type.

edit: posting your entire class would help =)

Code:

---

final JTextArea TextArea = new JTextArea("Hello",5,20);

---

Thanks much

Please make a habbit of naming variables without capitals, and also declare the variable all the way, such as this:

private final JTextArea textArea = new JTextArea("Hello", 5, 20);

You will understand why once you program some more :)
Cheers

Quote:

---

Originally Posted by fex

Please make a habbit of naming variables without capitals, and also declare the variable all the way, such as this:

private final JTextArea textArea = new JTextArea("Hello", 5, 20);

You will understand why once you program some more :)
Cheers

---

Thanks.

In fact I always do that, this was a rare example.

I got used to that in .NET because they were automatically defined as so:

textBox1
webBrowser1
richTextBox1
etc.

Ah, good to hear :)

Btw, I don't know what Java editor you are using, but a somewhat smarter editor would have noticed that you needed to make the variable final. Or maybe you just didn't see it because you 're new to Java...

Hello everyone,

Now I want to use the text in a text field!!

So, for example,

I have a textfield and what to define the text that is there to a variable.

1. User Inputs text;
2. User presses button;
3. Program stores the text in the JTextField to a variable;
4. ...

How to do it?

Have you gone through the Oracle Swing tutorials on how to use text fields, buttons and action listeners? If not, you need to start there.

I already got it.

It's textField.getText() :D

Have you ever heard of an API ? All the methods that you can perform on a class object are listed there...
Java Platform SE 6