Question

I created a dialog box in Swing for editing data. It contains a JTextArea, two JButton instances (OK & Cancel) and a JCheckBox (Wrap Text). What I wanted to do is to have the text in the text area wrapped whenever the user clicks on the check-box. I initially have the text wrapped by using setLineWrap(true).

I am using the following code:

    Runnable r1=new Runnable() {
        @Override
        public void run() {
            System.out.println("True");
            keyField.setLineWrap(true);
            keyField.requestFocus();
        }
    };

    Runnable r2=new Runnable() {
            @Override
            public void run() {
               System.out.println("FALSE");
               keyField.setLineWrap(false);
               keyField.repaint();
               keyField.requestFocus();
            }
     };
    final Thread t1=new Thread(r1) ;
    final Thread t2=new Thread(r2);

    final JCheckBox chkSwing = new JCheckBox("Word Wrap",true);

    chkSwing.addItemListener(
            new ItemListener() {
                @Override
                public void itemStateChanged(ItemEvent e) {
                    //To change body of implemented methods use File | Settings | File Templates.
                    if (e.getStateChange() == ItemEvent.SELECTED) {
                        t1.start();
                    } else if (e.getStateChange() != ItemEvent.SELECTED){
                        t2.start();
                    }
                }
            });

    panel.add(chkSwing);

The Problem

The problem is that once I deselect the check-box, the text gets unwrapped, but again checking the check-box does not wrap the text again. The console shows that the thread is being called. How to make the check-box work for setting/unsetting the word wrap behavior of the text-area?

Answer 1

There is no reason to start separate Threads. Even worse, you should not modify Swing components on the non-EDT. See the Concurrency in Swing tutorial

chkSwing.addItemListener(
  new ItemListener() {
    @Override
    public void itemStateChanged(ItemEvent e) {
       keyField.setLineWrap( e.getStateChange() == ItemEvent.SELECTED );
    }
  } );

will do it.