Java Swing jpanel paint方法执行两次的问题

Java Swing jpanel paint方法执行两次的问题：

在其他环境下执行了两次，自己测试怎么都是执行了一次，记录一下这个问题；需要后继工作；

可能是进行各种参数设置的时候导致了paint方法的调用；

在调试过程中，发现repaint方法会因为各种情况不断的调用；注意JFrame和JPanel是不一样的哦；

package com.srie.test;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
public class JFrame002 extends JFrame {
    private static final long serialVersionUID = 1L;
    private JPanel contentPane;
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    JFrame002 frame = new JFrame002();
                    frame.setSize(80, 60);
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    /**
     * Create the frame.
     */
    public JFrame002() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel() {
            private static final long serialVersionUID = 1L;
            int j = 10000;
            // 如果override paint方法，就不会执行paintComponent方法
            @Override
            public void paint(Graphics g) {
                System.out.println("com.srie.test.JFrame002.JFrame002().new JPanel() {...}.paint(Graphics):" + j++);
            }
            @Override
            protected void paintComponent(Graphics g) {
                System.out.println("com.srie.test.JFrame002.JFrame002().new JPanel() {...}.paintComponent(Graphics):" + j++);
            }
            @Override
            public void update(Graphics g) {
                System.out.println("com.srie.test.JFrame002.JFrame002().new JPanel() {...}.update(Graphics):" + j++);
            }
            @Override
            public void repaint() {
                // 最开始打印的时候，j输出的竟然是0，在4种初始化之后，才把j初始化了；
                System.out.println("com.srie.test.JFrame002.JFrame002().new JPanel() {...}.repaint():" + j++);
            }
        };
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        // 这个会增加一次repaint方法的调用；
        contentPane.setFont(null);
        // contentPane.setMinimumSize(new Dimension(10, 10));
        setContentPane(contentPane);
    }
    int i = 0;
    // 这个放开了之后，里面的内容都不进行重绘了；只是在初始化的时候里面repaint了6次；
    // @Override
    // public void paint(Graphics g) {
    // System.out.println("com.srie.test.JFrame002.paint(Graphics):" + i++);
    // }
    // 这个不是paintComponent，多了一个s哦；是java.awt.Container的方法；
    @Override
    public void paintComponents(Graphics g) {
        System.out.println("com.srie.test.JFrame002.paintComponents(Graphics):" + i++);
    }
    @Override
    public void update(Graphics g) {
        System.out.println("com.srie.test.JFrame002.update(Graphics):" + i++);
    }
    @Override
    public void repaint() {
        System.out.println("com.srie.test.JFrame002.repaint():" + i++);
    }
}

参考：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import javax.swing.*;
public class SimpleGui3C implements ActionListener {
    JFrame frame;
    public static void main(String[] args) {
        SimpleGui3C gui = new SimpleGui3C();
        gui.go();
    }
    public void go() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JButton button = new JButton("Change colors");
        button.addActionListener(this);
        MyDrawPanel drawPanel = new MyDrawPanel();
        frame.getContentPane().add(BorderLayout.SOUTH, button);
        frame.getContentPane().add(BorderLayout.CENTER, drawPanel);
        frame.setResizable(false);
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
    @Override
    public void actionPerformed(ActionEvent arg0) {
        frame.repaint();
    }
    class MyDrawPanel extends JPanel {
        private static final long serialVersionUID = 1L;
        public void paintComponent(Graphics g) {
            Graphics2D g2d = (Graphics2D) g;
            int red = (int) (Math.random() * 255);
            int green = (int) (Math.random() * 255);
            int blue = (int) (Math.random() * 255);
            Color startColor = new Color(red, green, blue);
            red = (int) (Math.random() * 255);
            green = (int) (Math.random() * 255);
            blue = (int) (Math.random() * 255);
            Color endColor = new Color(red, green, blue);
            GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
            g2d.setPaint(gradient);
            g2d.fillOval(70, 70, 100, 100);
            System.out.println(new Date());
        }
    }
}