问Main必须是astract，侦听器的ActionPerformed方法问题

EN

// Java program to create a blank text
// field of definite number of columns.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class Main extends JFrame implements ActionListener {
    // JTextField
    static JTextField t;

    // JFrame
    static JFrame f;

    // JButton
    static JButton b;

    // label to diaplay text
    static JLabel l;

    // default constructor
    Main()
    {
    }

    // main class
    public static void main(String[] args)
    {
        // create a new frame to stor text field and button
        f = new JFrame("textfield");

        // create a label to display text
        l = new JLabel("nothing entered");

        // create a new button
        b = new JButton("submit");

        // create a object of the text class
        Main te = new Main();

        // addActionListener to button
        b.addActionListener(te);

        // create a object of JTextField with 16 columns
        t = new JTextField(16);

        // create a panel to add buttons and textfield
        JPanel p = new JPanel();

        // add buttons and textfield to panel
        p.add(t);
        p.add(b);
        p.add(l);

        l.setOpaque(true);
        // add panel to frame
        f.add(p);

        // set the size of frame
        f.setSize(300, 300);

        p.setBackground(Color.cyan);

        f.show();
    }

    // if the button is pressed
    public void actionPerformed(java.awt.event.ActionEvent e, JPanel p)
    {
        String s = e.getActionCommand();
        if (s.equals("submit")) {
            // set the text of the label to the text of the field
            if(t.getText().equals("hue")) {

                p.setBackground(changeColor());
            }
            l.setText(t.getText());

            // set the text of field to blank
            t.setText(" ");
        }
    }
    public Color changeColor() {
        int r = (int)(Math.random())*256;
        int g = (int)(Math.random())*256;
        int b = (int)(Math.random())*256;
        Color color = new Color(r,g,b);
        return color;
    }
}