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Thread: Question about thread

  1. #1
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    Default Question about thread

    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


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Question about thread

    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.
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  3. #3
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    Default Re: Question about thread

    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

  4. #4
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Question about thread

    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.
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  5. #5
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    Default Re: Question about thread

    That what I wanted to know
    Thank you so much KevinWorkman for your help
    Last edited by Suzie_K; May 4th, 2012 at 01:47 PM.

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