Question

I have one frame in which one TestArea is there. When I append some string from this class then String is appended but when I want to append String from other class then String is not appended. I created one method to append string in TextArea, when I call this method in this class then string is appended on text Area. But when I call this method from other Class then String is not appended on TextArea.

Code (MainClass):

public class MainClass {
private JFrame frame;
private TextArea textArea;
private Font font;
private JButton button1;
private JButton button2;
private SecondClass secondClass;

public MainClass() {
    try {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        frame = new JFrame("XXX");
        frame.setBounds(200, 200, 600, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        button1 = new JButton("Button1");
        font = new Font("Arial", Font.BOLD, 13);
        button1.setFont(font);
        button1.setBounds(4, 4, 289, 30);

        button2 = new JButton("Button2");
        button2.setFont(font);
        button2.setBounds(300, 4, 289, 30);

        font = null;

        textArea = new TextArea();
        textArea.setBounds(4, 38, 585, 322);
        textArea.setEnabled(true);

        font = new Font("Arial", Font.PLAIN, 13);
        textArea.setFont(font);

        frame.add(button1);
        frame.add(button2);
        frame.add(textArea);

        button1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                textArea.append("*** I am in actionPerformed() ***\n");
                appendToTextArea("Call from actionPerformed() method\n");
            }
        });

        button2.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                secondClass = new SecondClass();
                secondClass.printOnTextArea();
            }
        });

    } catch (Exception e) {
        textArea.append(e.toString());
    }
}

public void appendToTextArea(String str) {
    System.out.println(str+"\n");

    textArea.append(str+"\n"); //this line not work when I call this method from other class
}

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            MainClass window = new MainClass();
            window.frame.setVisible(true);
        }
    });
}

}

Code(SecondClass):

import com.grissserver.MainClass;

public class SecondClass extends MainClass{
void printOnTextArea() {
    System.out.println("*** printOnTextArea() ***");
    super.appendToTextArea("call from Second Class in printOnTextArea()");
}
}

Please give some Idea, why this is not working.

Answer 1

The SecondClass has its own textArea. So you may need to pass MainClass‘s textArea to SecondClass.

public class SecondClass {
    private TextArea tArea;
    SecondClass(TextArea ta) {
        tArea = ta;
    }
    void printOnTextArea() {
        System.out.println("*** printOnTextArea() ***");
        tArea.append("call from Second Class in printOnTextArea()");
    }
}

You should change your MainClass like this.

....
button2.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent arg0) {
        secondClass = new SecondClass(textArea);
        secondClass.printOnTextArea();
    }
});
....

hope this helps…