如何将 JSpinner 值从 Java class 传递给另一个 Java class

Question

I have very poor knowledge of Java, especially in terms of classes. I have a class that has a public static JSpinner with SpinnerNumberModel(2, 2, 4, 1) . After updating the value in the JSpinner (2, 3 or 4), after pressing the JButton (separate class), it must be passed to the same JButton. But only the value that I have already set as default is passed, ie 2. After searching all possible forums, I realized that the problem might be in the static modifier. However, without this modifier, the error "Non-static field 'JSpinner_name' cannot be referenced from a static context" appears. The code of the class in which the JSpinner is located:

public class settingsPanel extends JPanel {
    public static JSpinner playersCount = new JSpinner(new SpinnerNumberModel(2, 2, 4, 1));
    
    public void main(){

        //some code with JSpinner change listener

        add(playersCount);
        saveSettingsButton saveSettingsButton = new saveSettingsButton();
        add(saveSettingsButton);
        saveSettingsButton.main();
    }
}

The class code to which I need to pass values from JSpinner:

public class saveSettingsButton extends JButton {
    public void main(){

        //some code

        addActionListener(e -> {
            int errorChecking = 0;
            switch ((int) settingsPanel.playersCount.getValue()) {

                //some code

        });
    }
}

I want to pass settingsPanel.playersCount.getValue() to the saveSettingsButton class, but as I described above, only the predefined value is passed. I tried to create a method but still not working (maybe i'm a noob at methods). How to make available updated value from JSpinner in another class?

Answer 1

Java tutorials often expect users to "extend" user interface classes to use them. This is great in theory, but in practice, often leads to over kill, especially for first-timers.

Here's a simple program using your components which allows the button to read values from your spinner.

I've added comments to explain what each component of the app is doing and why it's doing it.

package com.company;

import javax.swing.*;

public class MyApp {
    // Declare the UI components we plan on using
    // Note: Without "private" or "public" modifiers
    //   they'll default to "package private", which
    //   is a sane default.
    JFrame mainFrame;
    JPanel settingsPanel;
    JButton saveSettingsButton;
    JSpinner playersCount;

    public MyApp() {
        // Initialize our UI components
        mainFrame = new JFrame("My App");
        settingsPanel = new JPanel();
        saveSettingsButton = new JButton("Click Me");
        playersCount = new JSpinner(new SpinnerNumberModel(2, 2, 4, 1));

        // Add any listeners (such a "click" listener)
        saveSettingsButton.addActionListener(e -> {
            int errorChecking = 0;
            // The button can read the spinner because they're both declared within the same scope (same class)
            switch ((int) playersCount.getValue()) {
                default:
                        System.out.println((int)playersCount.getValue());
            };
        });

        // Add UI components to panel
        settingsPanel.add(playersCount);
        settingsPanel.add(saveSettingsButton);

        // Add panel to frame/window
        mainFrame.add(settingsPanel);

        // Show our UI
        mainFrame.pack(); // Automatically set size of frame to fit components
        mainFrame.setLocationRelativeTo(null); // Center frame on primary screen
        mainFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE); // Close the app when this window is closed
        mainFrame.setVisible(true);

        // Perform our initial action
        saveSettingsButton.doClick();
    }

    // This is the main entry point into the application when run
    // By default, applications are NOT synchronized onto the UI thread (known as the "Event Dispatch Thread")
    // UIs that aren't synchronized can flicker, crash and have weird behavior
    // SwingUtilities has two functions to synchronize, we'll use "invokeLater()" for this purpose. 
    public static void main(String ... args) {
        SwingUtilities.invokeLater(() -> new MyApp()); // invokeLater(): UI should always be created on EDT!
    }


}