使用Graphics出现.NullPointerException初五

[ljs34101130]

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;


public class StafffingWindow extends JFrame{
	private static JTextArea jtaDescription = new JTextArea();
	OperatingToSQL op = new OperatingToSQL();
	private static Graphics g;
	
	public StafffingWindow() {
		add(new paint());
	}

	public static void main(String[] args) {
		JFrame frame = new StafffingWindow();
		frame.pack();
		frame.setTitle("操作初始界面Vol 0.1");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
		frame.setLocationRelativeTo(null);
		
	}

	class paint extends JPanel{
		JButton select = new JButton("查询数据");
		JButton insert = new JButton("插入数据");
		JButton update = new JButton("更改数据");
		JButton delete = new JButton("删除数据");
		
		public paint() {
			select.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					JFrame win = new JFrame();
					//对jtaDescription进行设置
					jtaDescription.setLineWrap(true);
					jtaDescription.setWrapStyleWord(true);
					jtaDescription.setEditable(false);
					jtaDescription.setText(op.selectTable());
					win.setSize(200, 200);
					win.setTitle("Infomation");
					win.setVisible(true);
					win.setLayout(new BorderLayout());
					//将文本域放入win框架中
					win.add(jtaDescription, BorderLayout.CENTER);
//					win.add(setLabel(), BorderLayout.NORTH);
				}
			});
			
			insert.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					op.insert();
				}
			});
			
			update.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e){
					op.Update();
				}
			});
			
			delete.addActionListener(new ActionListener() {
				public void actionPerformed(ActionEvent e) {
					op.Delete();
				}
			});
			setLayout(new GridLayout(1,4));
			add(select);
			add(insert);
			add(update);
			add(delete);
			
		}
	}
	/** 有问题	*/
	protected static JPanel setLabel() {
		JPanel jlbl = new JPanel();
		jlbl.paintComponents(g);
		g.drawString("姓名", 0, 0);//这里报错
		g.drawString("性别", 200 / 3, 0);
		g.drawString("身份证号码", 200 / 3 * 2, 0);
		
		return jlbl;
	}
}

[gloomyfish]

你在哪里初始化了

private static Graphics g;

在JAVA Swing中获取图像设备Graphics有两种途径 1.通过override paint(Graphics g)方法或者paintComponent(Graphics g)方法 2.创建BufferedImage对象，从BufferedImage对象中获取图像设备Graphics 显然你没有这么做。所以你无法获取Graphics。

[ljs34101130]

好吧，是错误。打错了