文件写入和读取不工作 Java

Question

I am trying to make a simple GUI app that takes strings and a button and saves it to a file. When the app loads, the fields are populated with the values in the text file, which will look like this:

School Name
Selected Radio Button
Date

When I change the values in the GUI it will overwrite the above values in the text file. The program populates the gui fields by reading line by line.

As I have my program now it gets an array Index out of bounds exception and it does not save anything to the file.

here is the stacktrace:

  Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at prog24178.TestingFiles.<init>(TestingFiles.java:66)
    at prog24178.TestingFiles.main(TestingFiles.java:88)

here is the code:

public class TestingFiles extends JFrame {
    private JTextField txtCollege;
    private JTextField txtDate;
    public ArrayList <School> schools;
    String file = "c:\\Temp\\schools.txt";


    public TestingFiles(){
        super("Testing Files");
        getContentPane().setLayout(null);

        txtCollege = new JTextField();
        txtCollege.setBounds(0, 0, 359, 20);
        getContentPane().add(txtCollege);
        txtCollege.setColumns(10);

        JRadioButton selComp = new JRadioButton("Computers");
        selComp.setBounds(10, 27, 109, 23);
        getContentPane().add(selComp);

        JRadioButton selEng = new JRadioButton("Engineering");
        selEng.setBounds(139, 27, 109, 23);
        getContentPane().add(selEng);

        JRadioButton selArt = new JRadioButton("Arts");
        selArt.setBounds(281, 27, 78, 23);
        getContentPane().add(selArt);

        ButtonGroup bg = new ButtonGroup();
        bg.add(selArt);bg.add(selEng);bg.add(selComp);

        txtDate = new JTextField();
        txtDate.setBounds(0, 57, 359, 20);
        getContentPane().add(txtDate);
        txtDate.setColumns(10);

        JButton btnSave = new JButton("Save");
        btnSave.setBounds(0, 77, 183, 34);
        getContentPane().add(btnSave);
        btnSave.addActionListener(new SaveActionHandler());

        JButton btnExit = new JButton("Exit");
        btnExit.setBounds(183, 77, 176, 34);
        getContentPane().add(btnExit);
        btnExit.addActionListener(new ExitHandler());


        schools = new ArrayList <School>();
        try{
            File f = new File(file);
            Scanner s = new Scanner (f);
            while (s.hasNextLine()){
                String line  = s.nextLine();
                String [] fields = line.split("/n");
                //schools.add(new School(fields[0], fields[1], fields[2])); ***Array Index out of bounds
            }
            s.close();
        }
        catch (IOException ioe){}
    }


    class SaveActionHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            schools.add(new School(txtCollege.getText(),txtDate.getText() ));
        }       
    }
    class ExitHandler implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e) {
            System.exit(0);     
        }       
    }


    public static void main(String[] args) {
        TestingFiles app = new TestingFiles();
        app.setSize(375,150);
        app.setVisible(true);
        app.setDefaultCloseOperation(DISPOSE_ON_CLOSE);

    }
}
class School  {
    private String college;
    private String field;
    private String date;
    public School() {};
    public School(String college, String field,  String date){
        this.college = college;
        this.field = field;
        this.date = date;
    }
    public String getCollege() {
        return college;
    }
    public String getField() {
        return field;
    }
    public String getDate() {
        return date;
    }
    public void setCollege(String college) {
        this.college = college;
    }
    public void setField(String field) {
        this.field = field;
    }
    public void setDate(String date){
        this.date = date;
    }
}

Answer 1

Look at this code:

File f = new File(file);
Scanner s = new Scanner (f);
while (s.hasNextLine()){
    String line  = s.nextLine();
    String [] fields = line.split("/n");
...

You're getting a line from the file and then trying to split it on the newline character. Scanner#nextLine() by default gives you everything from its current position up to the next newline. In that case, a String returned by Scanner#nextLine() will never contain a newline, so your fields array will only ever contain one item, the entire line . So when you try to access fields[1] you get the exception.

An easy way you could have figured this out yourself, since you know the line that has the problem start there and work backwards to verify your assumptions. The first assumption you should verify is that fields contains the number of fields you expect.

String [] fields = line.split("/n");
System.out.println("fields contains " + fields.length + " items");

That would have told you that fields only contains one item.

The next assumption to verify would be that line actually contains newlines.

String line  = s.nextLine();
System.out.println("Line is " + line);

Ahh, there's the problem! line doesn't contain any newlines and you're trying to split on newlines.