我这里是一个简单的用户登录的程序，有两个Jpanel(pnlTop和主体部分)，主体部分有user的JPanel，PassWord的JPanel。
其中，用户的密码、用户名信息都是存储在"information"路径下的"Customer.txt"文件里面的。
isCorrect()和checkInput()属于自定义的方法，用于检查输入和文件内的信息是否匹配。
package UI;import java.awt.BorderLayout;import java.awt.Color;import java.awt.Dimension;import java.awt.Font;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.util.ArrayList;import java.util.List;import javax.swing.JButton;import javax.swing.JLabel;import javax.swing.JOptionPane;import javax.swing.JPanel;import javax.swing.JPasswordField;import javax.swing.JTextField;import javax.swing.border.EmptyBorder;import Controller.CustomerController;import Customer.Customer;import myComp.MyPicPanel;public class LoginForm extends BaseDialog{ private JPanel pnlMain = null; private JPanel pnlTop = null; private JPanel pnlUsername = null; private JPanel pnlPassword =null; private JPanel pnlButton = null; private JLabel lblUsername = null; private JLabel lblPassword= null; private JButton btnExit= null; private JButton btnLogin= null; private JTextField txtUsername= null; private JPasswordField txtPassword= null; public LoginForm(){ pnlTop = new MyPicPanel("images/2.jpg",400,90); pnlTop.setPreferredSize(new Dimension(400,90)); this.add(pnlTop, BorderLayout.NORTH); pnlMain = new JPanel(); pnlMain.setLayout(new BorderLayout()); pnlMain.setBorder(new EmptyBorder(5,0,0,0)); pnlMain.setBackground(Color.LIGHT_GRAY); this.add(pnlMain, BorderLayout.CENTER); initUI(); } public void initUI(){ //user name panel pnlUsername = new JPanel(); pnlUsername.setPreferredSize(new Dimension(this.getWidth(),60)); pnlUsername.setBorder(new EmptyBorder(10,0,0,0)); pnlMain.add(pnlUsername,BorderLayout.NORTH); //password panel pnlPassword = new JPanel(); pnlPassword.setPreferredSize(new Dimension(this.getWidth(),60)); pnlMain.add(pnlPassword,BorderLayout.CENTER); //button panel pnlButton = new JPanel(); pnlButton.setPreferredSize(new Dimension(this.getWidth(),60)); pnlMain.add(pnlButton,BorderLayout.SOUTH); addUsername(pnlUsername); addPassword(pnlPassword); addButton(pnlButton); } public ActionListener onclickListener = new ActionListener(){ @Override public void actionPerformed(ActionEvent e){ JButton jb = (JButton)e.getSource(); if(jb.getActionCommand().equals("login")){ if(checkInput()){ if(isCorrect()){ Mainform main = new Mainform(); dispose(); } }else{ JOptionPane.showMessageDialog(null, "登录失败","Gourmet Coffee System", JOptionPane.ERROR_MESSAGE); } }else if(jb.getActionCommand().equals("exit")){ System.exit(0); } } }; private void addPassword(JPanel pnlPassword) { JLabel lblPassword = new JLabel("Password"); lblPassword.setFont(new Font("Microsoft YaHei UI",Font.BOLD,20)); pnlPassword.add(lblPassword); txtPassword = new JPasswordField(10); pnlPassword.add(txtPassword); } private void addUsername(JPanel pnlUsername) { JLabel lblUsername = new JLabel("Account"); lblUsername.setFont(new Font("Microsoft YaHei UI",Font.BOLD,20)); pnlUsername.add(lblUsername); txtUsername = new JTextField(10); pnlUsername.add(txtUsername); } //默认FlowLayout private void addButton(JPanel pnlButton) { btnLogin = new JButton("Login"); btnLogin.setActionCommand("login"); btnLogin.addActionListener(onclickListener); pnlButton.add(btnLogin); btnExit = new JButton("Exit"); btnExit.setActionCommand("exit"); btnExit.addActionListener(onclickListener); pnlButton.add(btnExit); } public boolean isCorrect(){ boolean flag = true; CustomerController userManager = new CustomerController(); ArrayList customers = userManager.readObject("information","Customer.txt"); for(Customer customer: customers){ if(customer.getAccount().equals(txtUsername.getText().trim())) { if((String.valueOf(txtPassword.getPassword().equals(customer.getPassword()))) != null){ flag = true; } } } return flag; } public boolean checkInput(){ boolean flag = true; if(txtUsername.getText().trim().isEmpty()){ this.showMessage("账号不许为空！"); txtUsername.requestFocus(); flag = false; } if(String.valueOf(txtPassword.getPassword()).trim().isEmpty()){ this.showMessage("密码不许为空！"); txtPassword.requestFocus(); flag = false; } return flag; } public void showMessage(String msg){ JOptionPane.showMessageDialog(null, msg,this.getTitle(),JOptionPane.ERROR_MESSAGE); }}输出界面是这样：
但是每次输入用户名和密码（只要不是空，无论输入什么）都会报空指针异常。
这是异常片段：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at UI.Mainform.removeButton(Mainform.java:134) at UI.Mainform.(Mainform.java:71) at UI.LoginForm$1.actionPerformed(LoginForm.java:95)折磨了我整整一个下午加晚上…明天就要交了 求救啊各位大佬…… |
天盟APP下载
