存储从txt文件到字符串java的行

Question

My program reads a txt file and shows each line in a Jlabel when the Jbutton is clicked.

When the program runs and the Jbutton is clicked nothing appears in the JLabel.

I believe this is because I am not calling the String line correctly in the readFile method.

import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.*;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;

import javax.swing.*;

public class Driver {

        List<String> lines;

        static String line = "";

        static Scanner scanner = new Scanner(System.in);

        String s = "Welcome Students!";
        String b = "Start!";
        private JFrame f;
        private JPanel p;

        JFrame frame = new JFrame();

        JButton b1 = new JButton(b);

        JLabel jl = new JLabel(s);

        int i;

        private int clicked;

        public Driver() {
                gui();
        }

        public void gui() {
                lines = readLinesFromFile();
                i = 0;
                f = new JFrame("Flash Card Program");
                p = new JPanel();
                f.setLayout(new GridLayout(2, 1));
                f.add(jl);
                f.add(p);
                p.setLayout(new GridLayout(2, 1));
                p.add(b1);

                jl.setHorizontalAlignment(JLabel.CENTER);

                // pack the frame for better cross platform support
                f.pack();
                // Make it visible
                f.setVisible(true);
                f.setSize(500, 400); // default size is 0,0
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                b1.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e) {
                        jl.setText(lines.get(i));
                        i++;
                        if ( i > lines.size() ) {
                            i = 0;
                        }
                        if (b1.getText().equals("Click For Answer")) {
                            b1.setText("Next Question");
                        } else {
                            b1.setText("Click For Answer");
                        }
                    }
                });


            b1.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent e) {

                            if (clicked++ == 10) {

                                    Object[] options = { "No, thanks", "Yes, please" };

                                    int response = JOptionPane.showOptionDialog(frame,
                                                    "Would you like more math questions? ",
                                                    "Math Questions", JOptionPane.YES_NO_CANCEL_OPTION,
                                                    JOptionPane.QUESTION_MESSAGE, null, options,
                                                    options[1]);

                                    if (response == 1)
                                            clicked = 1; // reset
                                    else
                                            System.exit(0);
                            }
                    }
            }); 
    }


        public static List<String> readLinesFromFile() {
             List<String> lines = new ArrayList<String>();
            try {
                scanner = new Scanner(new File("upload.txt"));
                if (scanner.hasNext()){
                    lines.add(scanner.nextLine());
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            return lines;
        }

        private static void readFile(File file) throws FileNotFoundException{
            Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
            line = scanner.nextLine();
            }
            scanner.close();
        }


        public static void main(String[] args) {
            EventQueue.invokeLater(new Runnable() {
                @Override
                public void run() {
                    try {
                        new Driver();
                        readFile(new File("upload.txt"));
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
}

Answer 1

If you want to set the label for the jl field with one of the lines from the text file, then you need to do the following:

1. add a List field inside your Driver class:

    public class Driver { List<String> lines; //other fields that you need } 

2. in the gui() method, on the first line, initialize the lines field with the actual lines from the file, and initialize i counter with 0:

    public void gui() { lines = readLinesFromFile(); i = 0; //other code 

3. add the following method:

    public static List<String> readLinesFromFile() { List<String> lines = new ArrayList<String>(); try { Scanner scanner = new Scanner(new File("upload.txt")); if (scanner.hasNext()){ lines.add(scanner.nextLine()); } } catch (FileNotFoundException e) { e.printStackTrace(); } return lines; } 

4. change the first ActionListener for b1 with the following:

     b1.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { jl.setText(lines.get(i)); i++; if ( i > lines.size() ) { i = 0; } if (b1.getText().equals("Click For Answer")) { b1.setText("Next Question"); } else { b1.setText("Click For Answer"); } } }); 

Also, using this implementation, you don't need the line variable anymore, because you set the text for the label to one of the values from the lines field.

NOTE: if i gets higher that the actual number of lines in the file, it is reset to 0. If you don't want this, just change the if block in the ActionListener that checks the size