Question about thread

[Suzie_K]

Hi guys,
I am new in java programming ,
I wrote this pregame which is a simple GUI program with 2 buttons one to get the full date , and the other to get the time only .
I used Thread in this program in order to make the time update every 1 second.

here is the code :

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class GUI extends JFrame {
	private JButton B1;
	private JButton B2;
	private JLabel L1;
	private JPanel P1;
	private JPanel P2; 
	private MYThread TH;
	String S ="";
 
	public GUI (){
		super ("Time");
		TH = new MYThread();
		B1 = new JButton("Get full Time");
		B2 = new JButton("Get Time");
		L1 = new JLabel();
		P1 = new JPanel();
		P2 = new JPanel();
		P1.add(B1);
		P1.add(B2);
		P2.add(L1);
		add(P1 , BorderLayout.SOUTH);
		add(P2 , BorderLayout.CENTER);
		B1.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				try {
				 S = "1";
				 TH.start();
				}
				catch (IllegalThreadStateException e){
 
				 }	
			}
		});
		B2.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				 S = "2";
				 try {
				 TH.start();
				 }
				 catch (IllegalThreadStateException e){				 
				 }
			}
		});
	}
	class MYThread extends Thread{
		String T ;
		public void run() {
			super.run();
 
			while (true){
				if(S.equals("1")){
					Calendar C = new GregorianCalendar();
					T = C.getTime() + "";
 
					L1.setText(T);
					try {
						MYThread.sleep(1000);
					}
					catch (Exception e){					
					}
 
				}
				if(S.equals("2")){
					GregorianCalendar C = new GregorianCalendar();
					L1.setText(C.get(Calendar.HOUR)+":"+C.get(Calendar.MINUTE)+":"+C.get(Calendar.SECOND));
					try {
						MYThread.sleep(1000);
					}
					catch (Exception e){					
					}
				}
			}
		}
	}
}

My question is :
Can I use " TH.start(); " more than once in the same class ??
I used "TH.start() " in the Action Listener .

Sorry for my English

[KevinWorkman]

What happened when you tried? Also, you shouldn't have empty catch clauses. You're probably ignoring error messages that could help you understand what's going on.

You might want to use a Swing Timer instead of a thread. Updating the GUI on a thread other than the EDT is a big no-no.

[Suzie_K]

When I tried the program the first time it throw "java.lang.IllegalThreadStateException" ,
so that I tried to put it in a try catch blocks but I didn't know what to write in the Catch blocks so I left them empty !
the program works fine , but I don't know if this code is right or wrong !
thank you KevinWorkman

[KevinWorkman]

Sounds like you found out that you can't call Thread.start() more than once, which the API tells you: Thread (Java Platform SE 6)

By surrounding it by a try and a catch, you're simply ignoring the error. That's not the right thing to do.

But you shouldn't be using multiple threads to interact with the GUI like this anyway. Use a Swing Timer instead.

[Suzie_K]

That what I wanted to know
Thank you so much KevinWorkman for your help