存储从txt文件到字符串java的行

Question

我的程序读取txt文件，并在单击Jbutton时在Jlabel中显示每一行。

当程序运行并单击Jbutton时，JLabel中没有任何内容。

我相信这是因为我没有在readFile方法中正确调用String行。

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

如果要使用文本文件中的任一行设置jl字段的标签，则需要执行以下操作：

1. 在Driver类中添加一个List字段：

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

2. 在gui（）方法的第一行中，使用文件中的实际行来初始化lines字段，并使用0初始化i计数器：

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

3. 添加以下方法：

    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. 使用以下命令将b1的第一个ActionListener更改为：

     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"); } } }); 

同样，使用此实现，您不再需要line变量，因为您将标签的文本设置为lines字段中的值之一。

注意：如果我高于文件中的实际行数，则将其重置为0。如果您不希望这样做，只需更改ActionListener中的if块即可检查大小