我的程序读取一个txt文件,并在单击Jbutton时显示Jlabel中的每一行。
当程序运行并单击Jbutton时,JLabel中不会显示任何内容。
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();
}
}
});
}
}
答案 0 :(得分:0)
如果要使用文本文件中的一行设置 jl 字段的标签,则需要执行以下操作:
在Driver类中添加一个List字段:
public class Driver {
List<String> lines;
//other fields that you need
}
,在第一行,使用文件中的实际行初始化行字段,并初始化 i 计数器0:
public void gui() {
lines = readLinesFromFile();
i = 0;
//other code
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;
}
使用以下内容更改 b1 的第一个ActionListener:
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");
}
}
});
此外,使用此实现,您不再需要行变量,因为您将标签的文本设置为行中的一个值> field。
注意:如果 i 高于文件中的实际行数,则重置为0.如果您不想这样做,只需更改ActionListener中的if块检查大小