Thread: how to put changeable value in JTextField?

So, i made an applet w/ Eclipse, in which after every killed brick(or block) player gets 20 points.

In an applet points are counting well. Example there: applet in JFrame (I highlighted score values with red circles.)

But i cant figure out how to put that score value in a JTextField.

Main class of applet (parts where i am using value 'score'):

public class Main extends Applet implements Runnable, KeyListener
{
	public int score;
 
public void run(){
        ...
 
        if(blocks.get(i).alive == false){
			blocks.remove(i);
			score += 20;
         }
         ...
}}

JFrame class:

public class Window extends JFrame {
 
        private JFrame PaddleBricks;	
	public static Main app = new Main();
        public JTextField textField;
...
private void initialize() {
 
textField = new JTextField();
textField.setBounds(21, 114, 65, 20);
PaddleBricks.getContentPane().add(textField);
textField.setText(Integer.toString(app.score));
}}

I know that I only once set a 'score' value to that text field.
But I don't know how to make it changeable in a JTextField.
Should i use for/while cycle?
Maybe it is possible to make it changeable for example in every 3 seconds or something like that?

As u can see in this picture: applet in JFrame (I highlighted score values with red circles.)

Score on the top of an applet is ok, but in a textfield it stays at 0.

The only proper way to change the value of a JTextField is by calling the setText() method. I believe it has to do with the fact that JTextField are not constantly redrawing themselves, so changing the Strings that it may be displaying will not change what the JTextField displays. What you should do to fix this by using something called: event-driven programming.
To put it simply, you should create a method which updates your JTextField. Then, whenever you would like the value updated (perhaps every time the ball hits one of the squares), you would call the method.

NOTE: It is NEVER recommended to have a never-ending loop for the purpose of updating GUI elements. Using this practice will result in your program locking up and crashing.

it didn't work out.

Can you explain.
Try calling repaint() after setting the text.

You need to ask the questions:
1) What event happens that should cause the text field to update?
2) Where in my code does the event get handled?

Now, you said that the score is supposed to update every time the ball hits a brick. Post the section of your code that handles that event. I assume something should happen (other than the score updating) every time the ball hits a brick. That is where we want to call the setText() method from.

Where do you call any methods to change the contents of the text field where the data is displayed?

Ok, so you want to call the setText() method whenever ball.intersects(block), right?

Originally Posted by aussiemcgr

Ok, so you want to call the setText() method whenever ball.intersects(block), right?

That's right.

so i declare in a ball class:

Window win = new Window();
Main app = new Main();

and tried to write this, right after that if:

win.textField.setText(Integer.toString(app.score));

but got errors when the ball hits a block (then applet freeze):

Exception in thread "Thread-1" java.lang.NullPointerException
 
	at Zaidimas.Ball.CheckCollision(Ball.java:61) 
//in method CheckCollision(), on the line: win.textField.setText(Integer.toString(app.score));
 
	at Zaidimas.Main.run(Main.java:169)  
//in method run(), on the line: ball.CheckCollision(blocks.get(i));
 
	at java.lang.Thread.run(Unknown Source)

java.lang.NullPointerException
at Zaidimas.Ball.CheckCollision(Ball.java:61)

Look at line 61 and find the variable that has a null value. If you can not see which variable is null, add a println just before line 61 that prints out the values of all the variables used on line 61. If this is the line:
win.textField.setText(Integer.toString(app.score)) ;
print out the values of: win, textfield and app

When you have found the variable with the null value, backtrack to see why it does not have a valid value.

Why is textField null?
Check that the code gives textField a value. Make sure their is only one variable named textField.

did you try calling repaint() for the GUI that the text field is shown in?
Otherwise you'll have to post the code for testing.

where i should call repaint()?
tried to put it, just after win.textField.setText(Integer.toString(app.score)) ; line:

win.textField.repaint();

Still, text field empty.


If i use textField.setText method in Window class, then textField isn't empty, and first value of score are set: 0.

edit:
it looks like the only way is to create a cycle or a method in Window class... but that is almost impossible, cuz i need a lot of values from other classes...

Zaidimas.Window[frame0,0,0,0x0,invalid,hidden,

Is there more than on instance of the class that the win variable points to? One is visible and the other, where the call to setText is going, is not.

Add a println to your Window (Window is a java SE class???) class's constructor so you can see how many instances of the class you create by the number of times the println prints out its message.

it's two times.
but my project works like that:
- firstly, the small window shows up with the button "play".
- after that buttont is clicked, the same window becames bigger (resize method) and an applet appears in that window.

So the first time window constructor is called when project starts, the second time when i click Play button.

window class extends JFrame. that is my GUI class.

I think you are looking at one window and setting the values for the hidden window.
Change the logic so you set the values for the window you are looking at.

ok, so i modify my Window class to minimum: no buttons, no menus, only that textfield and applet starts when Play button is clicked...

this is how it looks:

public class Window extends JFrame {
	public JFrame frame;
	Main app = new Main();	
	public JTextField textField;
 
	public static void main(String[] args) {
 
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Window window = new Window();					
					window.frame.setVisible(true);			
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}
 
	public void GameStart(){
 
		JPanel panel_1 = new JPanel();		
		panel_1.setBounds(130, 2, 440, 430);
		panel_1.setVisible(true);
		frame.getContentPane().add(panel_1);
		panel_1.add(app);
 
		app.init();		
		app.start();
		app.setVisible(true);
		app.setSize(440, 400);
		app.setBounds(0, 0, 440, 400);
 
	}
 
	public Window() {
		initialize();
		System.out.print("Window used" + "\n");
	}
 
	private void initialize() {
 
		frame = new JFrame();
		frame.setTitle("Žaidimas \"Paddle bricks\"");
		frame.setBounds(200, 100, 600, 520);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.getContentPane().setLayout(null);
 
		final JButton zaisti = new JButton("PLAY");
		zaisti.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				GameStart();
			}
		});		
		zaisti.setBounds(22, 11, 85, 27);
		frame.getContentPane().add(zaisti);
 
		textField = new JTextField();
		textField.setBounds(21, 114, 65, 20);
		textField.setVisible(true);
		frame.getContentPane().add(textField);
		}
}

actually, when i wrote this line "window.setVisible(true);" in a run method, another window shows up, but its empty, and that window do not call window constructor.
only when i click Play button to activate applet, window constructor is called second time...

Window is a Java SE class. Can you give your class a different name?

You can create as many instances of your window class as you want. If you want to see the contents of any component that is in a window, you need to change the component that is in the instance that is being shown.

Why extend JFrame and also have the variable: frame?

How many windows are needed?

How the class is defined depends on how you are using it. Normally one JFrame is enough.

an applet appears in the same window.

What do you mean by "applet"? Applet's run from HTML pages in browsers.