如何在jtextarea上附加文本

Question

When I push a button, I want to show text in a JTextArea before executing a method. I use jTextArea.append() and jTextArea.settext() but the text appears after method execution. My code:

    //...JTextArea jTextArea;
    JButton btnGo = new JButton("Start");
    btnGo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
        jTextArea.append("line before\n");
        myMethodFromOtherClass();
        jTextArea.append("line after\n");
        }
    }

Any sugestion?

Answer 1

The actionPerformed() method is dispatched by the EDT (Event dispatcher thread) which handles all GUI-related events. Updates performed within the method will not be updated until the actionPerformed() method completes execution. To solve this, perform myMethodFromOtherClass() in another thread, and only queue the final update event ( jTextArea.append("line after\\n"); ) after the method completes execution in the second thread.

A crude demonstration of this is shown below:

JButton btnGo = new JButton("Start");
btnGo.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e) {
        //Leave this here
        jTextArea.append("line before\n");

        //Create new thread to start method in
        Thread t = new Thread(new Runnable(){
            public void run(){
                myMethodFromOtherClass();

                //Queue the final append in the EDT's event queue
                SwingUtilities.invokeLater(new Runnable(){
                    public void run(){
                        jTextArea.append("line after\n");
                    }
                });
            }
        });

        //Start the thread
        t.start();
    }
}

Should a more elegant solution be devised please look at SwingWorker which is based on a very similar procedure but with more advanced features.