为什么此Java代码不起作用？

Question

What I want to do is very basic: I have an interface that contains a button; when I push that button, I want my program to read the next line from a text file and display it in a textfield. But nothing happens, and I have a feeling it's because it doesn't read my file correctly :\\ Please help, I'm a complete newbie in the Java world and I was even happy that I got rid of the compiler errors (yay me!) but this is worse, 'cause now I don't know what to google :))

package practice;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.InputStreamReader;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextArea;

public class MyApp extends JFrame {
    JButton button;
    JTextArea afisaj; 

    MyApp(){ 
        setTitle("MyApp");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
        init();
        setSize(500,500);
        setLocationRelativeTo(null); 
        setVisible(true); 
    }

    public void init(){
        this.setLayout(null);

        button = new JButton("Read more");
        afisaj = new JTextArea();

        button.setBounds(200,50,100,30); 
        add(button); 

        afisaj.setBounds(40,100,400,300);
        add(afisaj); 
    }

public static void main(String[] args){
    final MyApp m = new MyApp(); 

    File f = new File("C:\\myfile.txt");
    BufferedReader b = new BufferedReader(new InputStreamReader(System.in));   
    try{
    b = new BufferedReader(new FileReader(f));  
    }
    catch (FileNotFoundException e){System.out.println("error 1")}

    final BufferedReader bf = b; 

      m.button.addActionListener(new ActionListener(){     
      public void actionPerformed(ActionEvent e){
          String s = new String();        
          try{
                if ((s=bf.readLine())!= null){
                    m.afisaj.append(s);  
                }
            }
            catch (Exception ee){System.out.println("error 2")}   
      }      
    }); 

    try{
    bf.close(); 
    }
    catch (Exception e1){System.out.println("error 3")}; 

}

}

Answer 1

The problem is that the stream you define get closed in try block. So when you try to read it gives Stream is closed.

Answer 2

1、data can not be shared，bf in the click event does not get to the

final BufferedReader bf = b; 

2、Code is modified as follows to achieve your results

public static void main(String[] args) {
    final MyApp m = new MyApp();
    m.button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            File f = new File("C:\\myfile.txt");
            BufferedReader b = new BufferedReader(new InputStreamReader(
                    System.in));
            try {
                b = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException ee) {
            }

            String s = new String();
            try {
                while ((s = b.readLine()) != null) {
                    m.afisaj.append(s);
                }
                b.close();
            } catch (Exception ee) {
            }
        }
    });
}

Answer 3

You should close the stream, when you close the window. Now you close it after you registered the event listener for the button. And before you really press the button.

public static void main(String[] args) throws Exception {
  final MyApp m = new MyApp();

  File f = new File("myfile.txt");
  BufferedReader b = new BufferedReader(new InputStreamReader(System.in));
  b = new BufferedReader(new FileReader(f));

  final BufferedReader bf = b;

  m.button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
      String s = new String();
      try {
        if ((s = bf.readLine()) != null) {
          m.afisaj.append(s);
        }
      } catch (Exception ex) {
        throw new RuntimeException(ex);
      }
    }
  });

  m.addWindowListener(new WindowAdapter() {
    @Override
    public void windowClosing(WindowEvent e) {
      try {
        bf.close();
      } catch (Exception ex) {
        throw new RuntimeException(ex);
      }
    }
  });
}

And please stop swalowing exception. System wouls have told you, that stream is closed and the rest is very simple, once you have that information!