如何从不同的 class 修改 JTextfield 的文本？ （爪哇）

Question

I'm trying to make a calculator as practice (I'm pretty bad at Java), but now I face a problem that I can't fix. I have a frame with a CardLayout, and on one of those cards is a JTextfield. I made the textfield in my main class: JTextField textfield = new JTextField(); , and did some things with it:

textfield.setBounds(50, 130, 380, 60);
textfield.setEditable(false);
textfield.setFont(font);

Now, I want to modify the text on the textfield from a different class (which makes the calculator work): main.textfield.setText(main.textfield.getText() + "ans"); , but that doesn't work. I am trying to modify the text in an ActionPerformed method. Does anyone know what I am doing wrong?

I tried doing it via a method in my main class, and repainting and revalidating the frame and the panel, which both didn't work.

@DanielJunglas asked for more information so here we go:p. I'll all the code that could possibly have effect on my problem.

        frame.setBounds(700, 250, 500, 700);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(null);
        frame.setResizable(false);
        
        contPanel.setLayout(cards);   //set the cardlayout to the container panel
        contPanel.setBounds(0, 0, 500, 700);
        
        createBegPanel();   //creating the panels
        createNorPanel();
        createTriPanel();
        //createEquPanel();
        
        contPanel.add(beginPanel, "p1");
        contPanel.add(normalCalcPanel, "p2");
        contPanel.add(triCalcPanel, "p3");
        //contPanel.add(equCalcPanel, "p4");
        cards.show(contPanel, "p1");
        
        frame.add(contPanel);
        frame.setVisible(true);

public void createNorPanel() {   //these are the things i do with the textfield
        textfield.setBounds(50, 130, 380, 60);
        textfield.setEditable(false);
        textfield.setFont(font);

public void actionPerformed(ActionEvent e) {
        JButton source = (JButton)e.getSource();
        main.textfield.setText("test");

So any button is pressed, it should set the text of the textfield to 'text', but it doesnt. Is this enough info?

Thanks in advance!

Answer 1

I guess you never call actionPerformed .

If you have a button then you need to add an ActionListener to it that implements the method actionPerformed(ActionEvent e) .

It looks like you have a class that implements an ActionListener (which is generally not a good solution). In that case you have to add this as ActionListener to the button.

JButton b = new JButton();
b.addActionListener(this);

A better solution would be to add a separate ActionListener to each button.

JButton b = new JButton();
b.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        main.textfield.setText("test");
    }
});

ActionListener is a functional interface (it has only one method) wich means you could also use a Lambda expression.

b.addActionListener(e -> main.textfield.setText("test"));