java swing 的jPanel背景颜色能否设置为透明,代码怎么写

设置颜色：
把pan - pan6的Background设为Null，这样他们就变为透明的了，以后只需要改变inquestFrame的颜色就可以改变全部的颜色，代码如下：
// 设置整体布局
JPanel pan = new JPanel();
pan.setLayout(new GridLayout(6, 1));
pan.add(pan1);
pan.add(pan2);
pan.add(pan3);
pan.add(pan4);
pan.add(pan5);
pan.add(pan6);
pan.setBackground(null);
pan1.setBackground(null);
pan2.setBackground(null);
pan3.setBackground(null);
pan4.setBackground(null);
pan5.setBackground(null);
pan6.setBackground(null);
r1.setBackground(null);
r2.setBackground(null);
inquestFrame.setBackground(Color.LIGHT_GRAY);
inquestFrame.setContentPane(pan);
inquestFrame.setSize(300, 250);
inquestFrame.setVisible(true);

设置图片需要改的比较多，自己比较那不一样吧：
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.URL;

import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTextField;

public class Inquest {
JFrame inquestFrame;
JLabel lab1, lab2, lab3, lab4, lab5, lab6;
JTextField text1, text2, text4, text5, text6;
JRadioButton r1, r2;
JButton inqButton;

public Inquest() {
inquestFrame = new JFrame("教育经历管理系统-查询窗口");
MyPanel pan1 = new MyPanel();
lab1 = new JLabel("请输入编码:");
text1 = new JTextField(10);
inqButton = new JButton(" 查询");
inqButton.addActionListener(new ButtonHandler());
pan1.add(lab1);
pan1.add(text1);
pan1.add(inqButton);

MyPanel pan2 = new MyPanel();
lab2 = new JLabel("姓名:");
text2 = new JTextField(10);
pan2.add(lab2);
pan2.add(text2);

MyPanel pan3 = new MyPanel();
lab3 = new JLabel("性别:");
r1 = new JRadioButton("男");
r2 = new JRadioButton("女");
// 把两个单选按钮放到一个群组中，保持二选一
ButtonGroup group = new ButtonGroup();
group.add(r1);
group.add(r2);

pan3.add(lab3);
pan3.add(r1);
pan3.add(r2);
MyPanel pan4 = new MyPanel();
lab4 = new JLabel("单位:");
text4 = new JTextField(10);
pan4.add(lab4);
pan4.add(text4);

MyPanel pan5 = new MyPanel();
lab5 = new JLabel("职位:");
text5 = new JTextField(10);
pan5.add(lab5);
pan5.add(text5);

MyPanel pan6 = new MyPanel();
lab6 = new JLabel("年龄:");
text6 = new JTextField(10);
pan6.add(lab6);
pan6.add(text6);

// 设置整体布局
MyPanel pan = new MyPanel();
pan.setLayout(new GridLayout(6, 1));
pan.add(pan1);
pan.add(pan2);
pan.add(pan3);
pan.add(pan4);
pan.add(pan5);
pan.add(pan6);
pan.setBackground(null);
pan1.setBackground(null);
pan2.setBackground(null);
pan3.setBackground(null);
pan4.setBackground(null);
pan5.setBackground(null);
pan6.setBackground(null);
r1.setBackground(null);
r2.setBackground(null);

MyPanel pan0 = new MyPanel();
pan0.setPreferredSize(pan.getPreferredSize());
pan0.setLayout(null);
pan.setBounds(0, 0, pan.getPreferredSize().width, pan.getPreferredSize().height);
URL url = Inquest.class.getResource("Winter.jpg");
ImageIcon img = new ImageIcon(url);
JLabel lab = new JLabel(img);
lab.setBounds(0, 0, img.getIconWidth(), img.getIconHeight());
pan0.add(pan);
pan0.add(lab);
inquestFrame.setContentPane(pan0);
inquestFrame.pack();
inquestFrame.setVisible(true);

}

public static class MyPanel extends JPanel {
public void paint(Graphics g) {
paintChildren(g);
}
}

public void setBack() {
((JPanel) inquestFrame.getContentPane()).setOpaque(false);
// Winter.jpg这个图片的位置要跟当前这个类是同一个包下
URL url = Inquest.class.getResource("Winter.jpg");
ImageIcon img = new ImageIcon(url);

JLabel background = new JLabel(img);
inquestFrame.getLayeredPane().add(background, new Integer(Integer.MIN_VALUE));
background.setBounds(0, 0, img.getIconWidth(), img.getIconHeight());
}

class ButtonHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {

// 生成SQL语句
String s = "select * from information where id=" + "'" + text1.getText() + "'";

String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
String url = "jdbc:odbc:test";

// DB db = new DB(driver, url, "sa", "");
// ResultSet rs = db.query(s);
// try {
// while (rs.next()) {
// text2.setText(rs.getString(2));
// String sex = rs.getString(3);
// if (sex.trim().equals("男"))
// r1.setSelected(true);
// else
// r2.setSelected(true);
//
// text4.setText(rs.getString(4));
// text5.setText(rs.getString(5));
// text6.setText(rs.getString(6));
// }
// } catch (Exception e2) {
// e2.printStackTrace();
// }

}
}

public static void main(String args[]) {
new Inquest();
}

}

JPanel panel1,panel2;
panel1=new JPanel();
panel2=new JPanel();
panel1.setBackground(Color.green);

panel2.setOpaque(false);//就是这里！！把panel2的背景色设为透明的了

panel1.add(panel2);

可以了吧

设置Jpanel背景颜色代码：
jPanel1.setBackground(new java.awt.Color(R, G, B)); //这里的RGB代码是颜色代码