使用JButton，JSpinner等在JPanel上绘图

问题描述

因此，我正在尝试为学校制作一个图形界面，其中涉及一个JMenuBar，JSpinner和2个JButton。 在这些对象下面，我尝试绘制一个简单的矩形。 我已经尝试过在扩展JPanel的类中使用paintComponent方法，但它不会出现。

import java.awt.Dimension;
import java.awt.FlowLayout;

import javax.swing.JFrame;

public class A1 {

public final static int DEFAULT_WIDTH = 640;
public final static int DEFAULT_HEIGHT = DEFAULT_WIDTH /12*9;


public static void main(String[] args) {

    JFrame frame = new JFrame("A1");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(new Dimension(DEFAULT_WIDTH,DEFAULT_HEIGHT));
    frame.requestFocus();
    frame.setLayout(new FlowLayout());
    frame.setLocationRelativeTo(null);
    frame.setResizable(false);

    lePanel panel = new lePanel();
    frame.add(panel);

    frame.setJMenuBar(panel.getMenuBar());

    frame.setVisible(true);

}

}

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.SpinnerNumberModel;

public class lePanel extends JPanel {

JMenuBar menuBar;
JButton submit;
JButton check;
JSpinner spinner;

public String test;

public lePanel() {
    menuBar = new JMenuBar();
    menuBar.add(createFileMenu(new JMenu("File")));
    menuBar.add(createHelpMenu(new JMenu("Help")));

    spinner = new JSpinner(new SpinnerNumberModel(1, 1, 10, 1));
    add(spinner);

    submit = new JButton("Submit");
    add(submit);

    check = new JButton("Check");
    add(check);

    submit.addActionListener(new ActionListener()
    {

        @Override
        public void actionPerformed(ActionEvent e) {
            if(e.getSource() == submit)
            {
                test = spinner.getValue().toString();
                System.out.println("Spinner Submitted");
            }
        }

    });

    check.addActionListener(new ActionListener()
    {

        @Override
        public void actionPerformed(ActionEvent e) {
            if(e.getSource() == check)
            {
                JOptionPane.showMessageDialog(lePanel.this, test, "Information",JOptionPane.INFORMATION_MESSAGE);
            }
        }

    });
}

private JMenu createHelpMenu(JMenu jMenu) {
    JMenu menu = jMenu;
    JMenuItem helpItem = new JMenuItem("Help");
    menu.add(helpItem);
    return menu;
}

private JMenu createFileMenu(JMenu jMenu) {
    JMenu menu = jMenu;
    JMenuItem newItem = new JMenuItem("New");
    JMenuItem clearItem = new JMenuItem("Clear");
    JMenuItem chooseFileItem = new JMenuItem("Open");
    JMenuItem saveItem = new JMenuItem("Save");
    JMenuItem exitItem = new JMenuItem("Exit");

    exitItem.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            System.exit(0);
        }

    });

    menu.add(newItem);
    menu.add(clearItem);
    menu.add(chooseFileItem);
    menu.add(saveItem);
    menu.add(exitItem);
    return menu;
}

public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;
    g2.setColor(Color.red);
    g2.drawRect(200, 200, 50, 50);
}

public JMenuBar getMenuBar() {
    return menuBar;
}

}