让您的构造函数与 main 方法分开，并使其名称与您的类名相同（即 public Panel_Test 因为您的班级名称是 Panel_Test ）。

Have your constructor be separate from the main method, and have its name be the same as your class name (i.e. public Panel_Test since the name of your class is Panel_Test).

public class Panel_Test extends JFrame {
    public Panel_Test() {
        // code here
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Panel_Test();
            }
        });
    }
}

不要忘记对你进行Swing操作Event Dispatch Thread，使用 javax.swing.SwingUtilities 。

Don't forget to do your Swing operations on the Event Dispatch Thread, using javax.swing.SwingUtilities.