Having issues changing button text in Java Swing

Question

I'm trying to test ways to change a button's text via an actionlistener. Here's my code:

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class TCTBack implements ActionListener {

    JFrame frame;
    JPanel panel;
    JLabel label1;
    JButton button1;
    String turn;

    public TCTBack() {

        turn = "-";

        panel = new JPanel();
        panel.setSize(500, 500);

        frame = new JFrame();
        frame.setSize(500,500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(panel);

        panel.setLayout(null);

        label1 = new JLabel("Interactive Button Test");
        label1.setBounds(10,20,80,25);
        panel.add(label1);

        button1 = new JButton("Button");
        button1.setBounds(10,80,80,25);
        button1.addActionListener(this);
        panel.add(button1);

        frame.setVisible(true);

    }

    @Override
    public void actionPerformed(ActionEvent e) {

        switch (turn) {
            case "-" -> {
                turn = "X";
                button1.setText("X");
            }
            case "x" -> {
                turn = "O";
                button1.setText("O");
            }
            case "O" -> {
                turn = "-";
                button1.setText("-");
            }
        }

    }

    public static void main(String[] args) {

        new TCTBack();

    }

}

It changes the button's text once, but won't change it after I click the button again. My goal is to be able to change the button's text from the default value("-") to X, then to O, then back to -. Any help would be appreciated, thanks. Also, I'm a newbie at asking questions so if I'm missing any information then just let me know.

Answer 1

Because you change the text to X but you check if it equals x

case "X" -> {
    ...
}

Answer 2

turn = "X"

case "x"

One is a capital X, and one is not.

Tip: If you think a switch is 'exhaustive' (a case statement should always be matched), add a default with throw new IllegalStateException(); or some such. Or use the switch as an expression, in which case java will give you that for free.

Answer 3

Define constants. Using constants prevents errors like yours.
Here are the parts of your code that I suggest you change with proposed changes. Explanations after the code.

public class TCTBack implements ActionListener {
    private static final String NONE = "-";
    private static final String O = "O";
    private static final String X = "X";

    public TCTBack() {
        button1 = new JButton(NONE);
    }

    public void actionPerformed(ActionEvent e) {
        String actionCommand = e.getActionCommand();
        String newVal;
        switch (actionCommand) {
            case NONE:
                newVal = X;
                break;
            case O:
                newVal = NONE;
                break;
            case X:
                newVal = O;
                break;
            default:
                newVal = null;
                JOPtionPane.showMessageDialog(frame,
                                              actionCommand,
                                              "Unhandled",
                                              JOptionPane.WARNING_MESSAGE);
        }
        if (newVal != null) {
            button1.setActionCommand(newVal);
            button1.setText(newVal);
        }
    }
}

When you create a JButton using the constructor that accepts a single, String argument, you set both the button's text and its action command . The ActionEvent object passed to method actionPerformed() contins this action command string.

However, calling method setText() of class JButton does not change the action command , hence you need to also update that via method setActionCommand() .