JTextArea can't append

Question

I need to append text to a JTextArea from a different class than the JTextArea is in. For example, my code is as follows:
public JTextArea getJTextArea() {
if (jTextArea == null) {
jTextArea = new JTextArea();
jTextArea.setBounds(new java.awt.Rectangle(115,8,274,181));
jTextArea.setBorder(javax.swing.BorderFactory.createLineBorder(java.awt.Color.gray,1));
jTextArea.setText("Chat initiated...");
jTextArea.append("append");
          return jTextArea;
Appending the text works in the above code, but if I try to append text using this code:
jTextArea.append("appended text");
anywhere else in the code it will not work. Why is this and how do I append text to the jTextArea?

Answer 1

You can't expect one class to recognize a variable declared elsewhere, right?
class Freader {
    public static void main(String args[]){
        jTextArea.append("new text"); //out of nowhere!
}This really isn't a Swing question, it's a "how can I write code" question.
To send message append (for example) to object jTextArea
and do this from within method m of class C, then either:
1. Create the object referred to by jTextArea in method m.
2. Have jTextArea passed into method m
3. Have jTextArea be a field of class C
4. Invoke some other method that returns the reference to jTextArea.
5. Don't do this directly in m: invoke another method that does
it directly or indirectly.
Do you get the idea?
For example, Below I define Main, which will invoke append, and Display,
which has the append method.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Main {
    public static void main(String[] args) {
        final JFrame f = new JFrame("Main");
        JButton btn = new JButton("append");
        btn.addActionListener(new ActionListener(){
            Display display = new Display(f);
            public void actionPerformed(ActionEvent evt) {
                display.append("some more text\n");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(btn);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
class Display {
    public Display(JFrame owner) {
        JDialog dialog = new JDialog(owner, "Display");
        textComponent = new JTextArea(20, 50);
        dialog.getContentPane().add(new JScrollPane(textComponent));
        dialog.pack();
        dialog.setVisible(true);
    public void append(String text) {
        textComponent.append(text);
    private JTextArea textComponent;
}