refresh label

[Ivan Kesic]

How to refresh label with for loop?

    

for (int i=0;i<10;i++)
jLabel.setText(""+i);

always throws nullexeption, and i cant figure why  :argh: 

[Rob Spoor]

Where and how do you initialize your variable jLabel?

[Michael Dunn]

is this the same problem as your other post

https://coderanch.com/t/433458/Swing-AWT-SWT-JFace/java/Display-real-time

[Ivan Kesic]

Michael Dunn wrote:is this the same problem as your other post

https://coderanch.com/t/433458/Swing-AWT-SWT-JFace/java/Display-real-time

Yes it almost is! But i am not sure that that other post is understandible! Maybe i should write this as a new question there?

[Michael Dunn]

it would be better to post your code so we can compile/run and see exactly what you are doing.
don't post your entire code, strip all unrelated stuff - menu's and other components not in the 'flow' of the problem.

make sure, after stripping, it compiles, runs, and produces the same problem - then post that

[Ivan Kesic]

   


import javax.swing.SwingUtilities;
import javax.swing.JPanel;
import javax.swing.JMenuItem;
import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.Rectangle;
import javax.swing.JLabel;


public class Gui {

	private JFrame jFrame = null;
	private JPanel jContentPane = null;
	private JButton butButton = null;
	private JLabel labLabel = null;
	

	
	private JFrame getJFrame() {
		if (jFrame == null) {
			jFrame = new JFrame();
			jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			
			jFrame.setSize(300, 200);
			jFrame.setContentPane(getJContentPane());
			jFrame.setTitle("Application");
		}
		return jFrame;
	}

	
	private JPanel getJContentPane() {
		if (jContentPane == null) {
			labLabel = new JLabel();
			labLabel.setBounds(new Rectangle(50, 35, 194, 58));
			labLabel.setText("");
			jContentPane = new JPanel();
			jContentPane.setLayout(null);
			jContentPane.add(getButButton(), null);
			jContentPane.add(labLabel, null);
		}
		return jContentPane;
	}

	
	
//  here i start my metod

	private JButton getButButton() {
		if (butButton == null) {
			butButton = new JButton();
			butButton.setBounds(new Rectangle(58, 110, 177, 46));
			butButton.setText("start");
			butButton.addActionListener(new java.awt.event.ActionListener() {
				public void actionPerformed(java.awt.event.ActionEvent e) {
					Gui gui = new Gui();
					gui.loop();
				}
			});
		}
		return butButton;
	}

//  here is the metod that i cant solve to work!

	public void loop(){
		for (int i=0;i<10;i++)
			labLabel.setText("Number: "+i);
	}
	
	
	public static void main(String[] args) {
		SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				Gui application = new Gui();
				application.getJFrame().setVisible(true);
			}
		});
	}

}

 

[Michael Dunn]

it's because of the way you call loop()
you create a new Gui(), then call loop(), so your new Gui() is effectively initialized like this

    
import javax.swing.SwingUtilities;
import javax.swing.JPanel;
import javax.swing.JMenuItem;
import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.Rectangle;
import javax.swing.JLabel;

class Gui {

  private JFrame jFrame = null;
  private JPanel jContentPane = null;
  private JButton butButton = null;
  private JLabel labLabel = null;

  public void loop(){
    for (int i=0;i<10;i++)
      labLabel.setText("Number: "+i);
  }
}

where labLabel is null

to fix, change the button's actionPerformed to this

//Gui gui = new Gui();
//gui.loop();
loop();

[Ivan Kesic]

Thank you very much!

But i still have a big problem!
I implanted sleep so its now like a timer! But, it only update, refresh labLabel Text at the end of the loop, ofcourse number 9, not every turn of it.(if i put System.out.println(i) it works fine in console, so i figure it has something to do with jlabel refreshing)

i tryed to put labLabel.repaint(); below abLabel.setText("Number: "+i); but nothing is happening.

   
public void loop(){
		Thread t = new Thread();
		
		for (int i=0;i<10;i++){
			
					labLabel.setText("Number: "+i);
					
		
		try {

			t.sleep(1000);

		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
			}
		}

 

[

[Michael Dunn]

your thread is not going to do anything - it has no run()

read this (particularly updating swing components via SwingUtilities.invokeLater(..))

http://java.sun.com/javase/6/docs/api/javax/swing/package-summary.html#threading

the easiest way for you to do what you want is to use a Swing Timer (does all the background threading for you)
you could also use a SwingWorker

[Ivan Kesic]

Thank you Michael, ill look into it