从其他选项卡更改JLabel的文本

Question

I can't seem to change a JLabel's text from another tab.

For example: Tab 1 has:

    JLabel headerLbl = new JLabel("Original Title");
    headerLbl.setSize(275, 40);
    headerLbl.setLocation(75, 10);
    headerLbl.setFont(new Font("Serif", Font.PLAIN, 28));
    headerLbl.setForeground(Color.BLUE);
    firstPanel.add(headerLbl);

Then Tab 2 would be an options tab where you can change the text of headerLbl. My code so far is:

private void initializeOptionsTab()
  {
    JPanel optionsPanel = new JPanel();
    optionsPanel.setLayout(null);

    JLabel headerLbl = new JLabel("Change Name To:");
    headerLbl.setSize(150, 25);
    headerLbl.setLocation(150, 15);
    optionsPanel.add(headerLbl);

    this.compTxtFld = new JTextField();
    this.compTxtFld.setSize(200, 20);
    this.compTxtFld.setLocation(120, 45);
    optionsPanel.add(this.compTxtFld);

    JButton setNewNameButton = new JButton("Set New Name");
    setNewNameButton.setSize(130, 25);
    setNewNameButton.setLocation(150, 85);
    optionsPanel.add(setNewNameButton);


    setNewNameButton.addActionListener(new ActionListener() 
    { 
        public void actionPerformed(ActionEvent e) 
        { 
            FrameMain.this.setNewNameButtonClick(); 
        }

    });
    this.tabbedPane.addTab("Options", optionsPanel);
  }

Then the code for the Button is:

private void setNewNameButtonClick()
  {
    setTitle(this.compTxtFld.getText());

    headerLbl.setText(this.compTxtFld.getText());
  }

So this gives me a Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException for lines

My guess is I cannot access the headerLbl in tab 1 from tab 2. What do I need to do to access it?

Answer 1

First of all it's a bad idea to have 2 labels both named headerLbl even though they are in different methods because it can cause confusion as you are coding.

The easiest solution I can think of is to declare headerLbl as a class variable

So like this:

public class FrameMain{
     JLabel headerLbl = new JLabel();
   //The rest is the same

}

and then inside your second method, change the name of headerLbl to something like changeNameLbl or something... so they don't conflict