Java添加图片出现空指针异常

CodeAnt626 2019-06-11 03:36:31

代码如下，有没有大佬帮忙看看是哪里出了问题呀

package view;



import java.awt.*;

import java.awt.event.*;

import javax.swing.*;



public class LoginView extends JFrame implements ActionListener {



	//定义组件

	ImageIcon welcomeIcon;

	JButton jb1,jb2,jb3;

	JPanel jp1,jp2,jp3,jp4;

	JTextField jtf;

	JPasswordField jpf;

	JLabel jlb1,jlb2,jlb3;

	

	//设定用户名和密码

	final String id="root";

	final String pwd="root";

	

	public LoginView(){

		//创建组件

		

		jb1=new JButton("登录");

		jb2=new JButton("重置");

		jb3=new JButton("退出");

		welcomeIcon=new ImageIcon(".src/images/welcome.jpg");

		

		//设置监听

		jb1.addActionListener(this);

		jb2.addActionListener(this);

		jb3.addActionListener(this);

		

		jp1=new JPanel();

		jp2=new JPanel();

		jp3=new JPanel();

		

		jlb1=new JLabel("用户名:");

		jlb2=new JLabel("密     码:");

		jlb3=new JLabel(welcomeIcon,JLabel.CENTER);

		

		jtf=new JTextField(10);

		jpf=new JPasswordField(10);

		

		//加入到JPanel中

		jp4.add(jlb3);

		

		jp1.add(jlb1);

		jp1.add(jtf);

		

		jp2.add(jlb2);

		jp2.add(jpf);

		

		jp3.add(jb1);		//添加按钮

		jp3.add(jb2);

		jp3.add(jb3);

		

		//加入JFrame中

		this.add(jp4);

		this.add(jp1);

		this.add(jp2);

		this.add(jp3);

		

		

		this.setLayout(new GridLayout(4,1));	//选择GridLayout布局管理器

		this.setTitle("长途汽车MIS");

		this.setSize(300, 200);

		this.setLocation(400, 200);

		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		this.setVisible(true);

		this.setResizable(true);

	}

	

	@Override

	public void actionPerformed(ActionEvent e) {

		// TODO 自动生成的方法存根

		if(e.getActionCommand()=="登录"){

			login();

		}else if(e.getActionCommand()=="重置") {

			clear();

		}else if(e.getActionCommand()=="退出") {

			System.exit(0);

		}

	}

	

	public void login() {

		if(id.equals(jtf.getText())&&pwd.equals(jpf.getText())) {

			JOptionPane.showMessageDialog(null, "登陆成功！","提示消息",JOptionPane.WARNING_MESSAGE);

			clear();

			dispose();

			UI ui=new UI();

		}else if(jtf.getText().isEmpty()&&jpf.getText().isEmpty()) {

			JOptionPane.showMessageDialog(null, "请输入用户名和密码!", "提示消息", JOptionPane.WARNING_MESSAGE);

		}else if(jtf.getText().isEmpty()) {

			JOptionPane.showMessageDialog(null, "请输入用户名!", "提示消息", JOptionPane.WARNING_MESSAGE);

		}else if(jpf.getText().isEmpty()) {

			JOptionPane.showMessageDialog(null, "请输入密码!", "提示消息", JOptionPane.WARNING_MESSAGE);

		}else {

			JOptionPane.showMessageDialog(null, "用户名或密码错误!\n请重新输入", "提示消息", JOptionPane.WARNING_MESSAGE);

			clear();

		}

	}



	public void clear() {

		jtf.setText("");

		jpf.setText("");

	}

}