Java GUI登录屏幕

Question

I have created a login screen for my Java GUI program, The login screen on a button click checks if the username and password that was entered in the textfields was equal to the lines in the text file and if it does it allows the user to move to the next screen, if not a JOptionPane.showMessageDialog will display. I also have another screen that allows the user to write to the file which inserts a new username and password.

Right so my problem is that it reads only the last 2 lines of code, so i am only able to login with the last created username and password. How do i go about making it read every single line to check for the username and password?

The main Login screen

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;

public class login extends JFrame {
  JButton blogin;
  JPanel loginpanel;
  JTextField txuser;
  JTextField pass;
  JButton newUSer;
  JLabel username;
  JLabel password;


  public login(){
    super("Login Autentification");

    blogin = new JButton("Login");
    loginpanel = new JPanel();
    txuser = new JTextField(15);
    pass = new JPasswordField(15);
    newUSer = new JButton("New User?");
    username = new JLabel("User - ");
    password = new JLabel("Pass - ");

    setSize(300,200);
    setLocation(500,280);
    loginpanel.setLayout (null); 


    txuser.setBounds(70,30,150,20);
    pass.setBounds(70,65,150,20);
    blogin.setBounds(110,100,80,20);
    newUSer.setBounds(110,135,80,20);
    username.setBounds(20,28,80,20);
    password.setBounds(20,63,80,20);

    loginpanel.add(blogin);
    loginpanel.add(txuser);
    loginpanel.add(pass);
    loginpanel.add(newUSer);
    loginpanel.add(username);
    loginpanel.add(password);

    getContentPane().add(loginpanel);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    Writer writer = null;
    File check = new File("userPass.txt");
    if(check.exists()){

      //Checks if the file exists. will not add anything if the file does exist.
    }else{
      try{
        File texting = new File("userPass.txt");
        writer = new BufferedWriter(new FileWriter(texting));
        writer.write("message");
      }catch(IOException e){
        e.printStackTrace();
      }
    }




    blogin.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        try {
          File file = new File("userPass.txt");
          Scanner scan = new Scanner(file);;
          String line = null;
          FileWriter filewrite = new FileWriter(file, true);

          String usertxt = " ";
          String passtxt = " ";
          String puname = txuser.getText();
          String ppaswd = pass.getText();


          while (scan.hasNext()) {
            usertxt = scan.nextLine();
            passtxt = scan.nextLine();

          }




          if(puname.equals(usertxt) && ppaswd.equals(passtxt)) {
            MainMenu menu =new MainMenu();
            dispose();
          } 
          else if(puname.equals("") && ppaswd.equals("")){
            JOptionPane.showMessageDialog(null,"Please insert Username and Password");
          }
          else {

            JOptionPane.showMessageDialog(null,"Wrong Username / Password");
            txuser.setText("");
            pass.setText("");
            txuser.requestFocus();
          }
        } catch (IOException d) {
          d.printStackTrace();
        }

      }
    });

    newUSer.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent e) {
        NewUser user = new NewUser();
        dispose();

      }
    });
  } 

}

And the new user file

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;

public class NewUser extends JFrame {
  JButton create;
  JPanel newUserPanel;
  JTextField txuserer;
  JTextField passer;


  public NewUser(){
    super("Registration");

    create = new JButton("Create");
    newUserPanel = new JPanel();
    txuserer = new JTextField(15);
    passer = new JPasswordField(15);


    setSize(300,200);
    setLocation(500,280);
    newUserPanel.setLayout (null); 


    txuserer.setBounds(70,30,150,20);
    passer.setBounds(70,65,150,20);
    create.setBounds(110,100,80,20);

    newUserPanel.add(create);
    newUserPanel.add(txuserer);
    newUserPanel.add(passer);

    getContentPane().add(newUserPanel);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);

    Writer writer = null;
    File check = new File("userPass.txt");
    if(check.exists()){

      //Checks if the file exists. will not add anything if the file does exist.
    }else{
      try{
        File texting = new File("userPass.txt");
        writer = new BufferedWriter(new FileWriter(texting));
        writer.write("message");
      }catch(IOException e){
        e.printStackTrace();
      }
    }




    create.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        try {
    File file = new File("userPass.txt");
    Scanner scan = new Scanner(file);;

      FileWriter filewrite = new FileWriter(file, true);

      String usertxter = " ";
      String passtxter = " ";
      String punamer = txuserer.getText();
      String ppaswder = passer.getText();
      while (scan.hasNext()) {
        usertxter = scan.nextLine();
        passtxter = scan.nextLine();
      }

        if(punamer.equals(usertxter) && ppaswder.equals(passtxter)) {
           JOptionPane.showMessageDialog(null,"Username is already in use");
          txuserer.setText("");
          passer.setText("");
          txuserer.requestFocus();

        } 
        else if(punamer.equals("") && ppaswder.equals("")){
        JOptionPane.showMessageDialog(null,"Please insert Username and Password");
        }
        else {
        filewrite.write(punamer+"\r\n" +ppaswder+ "\r\n");
        filewrite.close();
        JOptionPane.showMessageDialog(null,"Account has been created.");
        dispose();
        login log = new login();



        }
        } catch (IOException d) {
      d.printStackTrace();
    }

      }
    });
  } 

}

Answer 1

This:

if(puname.equals(usertxt) && ppaswd.equals(passtxt)) {
    MainMenu menu =new MainMenu();
    dispose();
} 

Needs to go inside of this:

while (scan.hasNext()) {
    usertxt = scan.nextLine();
    passtxt = scan.nextLine();
}

You're looping through the file with the while loop, but only testing the equality of the Strings after the while loop ends. This won't work as you're finding out.