满足条件时不显示 JOptionPane

Question

Im trying to make a Login Gui where it searches a text file for the password and username and if it doesn't find any that match the input then they display a JOptionPane but for some reason it never shows it. This is the code:

int determine=0;
try{
    String p1;
    String p2;
    String password =PasswordEntered.getText();
    String username =UsernameEntered.getText();
    FileReader reader=new FileReader("LoginPages.txt");
    FileReader read=new FileReader("LoginPages.txt");
    BufferedReader cr=new BufferedReader(read);
    BufferedReader br=new BufferedReader(reader);
   
    ArrayList<String> numbs = new ArrayList<String>();
    while (cr.readLine()!=null){
        numbs.add(br.readLine());
    }
    for (int i=0;i<=numbs.size();i=i+2){
        p1=numbs.get(i);
        p2=numbs.get(i+1);
        if(password.equals(p2)&&(username.equals(p1))) {
            determine=i;
            MainGUI x=new MainGUI();
            x.setVisible(true);
            dispose();
        } 
    }
    if (determine==numbs.size()) {
        JOptionPane.showMessageDialog(this, "try again");
    }
} catch(IOException ex){
    JOptionPane.showMessageDialog(this, "File Not Found");
}

It was supposed to pop up saying "try again" but instead it doesn't do anything. Please help or explain anyone.

Answer 1

The file is found, otherwise a JOptionPane would have shown up. You can test that by renaming the file and running the code again.

After that, the condition to display a JOptionPane would be determine==numbs.size() , but determine is initialized to zero and only set on successful login to the index at which it was found. Even if the last entry (pair of user/password) were found, it would match with i=size-2, so the condition never applies.

Change your code into something like

boolean found = false;
for (int i=0;i<=numbs.size();i=i+2){
    p1=numbs.get(i);
    p2=numbs.get(i+1);
    if(password.equals(p2)&&(username.equals(p1))) {
        found = true;
        break;
    } 
}
if (found) {
    MainGUI x=new MainGUI();
    x.setVisible(true);
    dispose();
} else {
    JOptionPane.showMessageDialog(this, "try again");
}