SwingJavatxt文件写入JTextArea

Question

有没有办法让文件末尾的空值消失？我决定在当循环之前追加第一行，这样它就不会受到\n的影响，但是这样做会出现空值...（没有第一个追加，它只是跳过第一行，开始在第二行打印）

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import javax.swing.event.*;
import java.io.*;

public class notepadMinus implements ActionListener{
    //Properties
    JFrame theFrame;
    JPanel thePanel;
    JMenuBar theBar;
    JMenu theMenu;
    JMenuItem openItem;
    JMenuItem saveItem;
    JTextArea theArea;
    JScrollPane theScroll;
    JFileChooser openChoose;
    String strLine;
    //Methods
    public void actionPerformed(ActionEvent evt){
        if(evt.getSource() == openItem){
            System.out.println("Open File");
            int intResult = openChoose.showOpenDialog(openItem);
            if(intResult == JFileChooser.APPROVE_OPTION){
                System.out.println("File selected");
                File selectedFile = openChoose.getSelectedFile();
                theArea.selectAll();
                theArea.replaceSelection("");
                try{
                    BufferedReader txtfile = new BufferedReader(new FileReader(openChoose.getSelectedFile()));
                    strLine = txtfile.readLine();
                    theArea.append(strLine);
                    while(strLine != null){
                        strLine = txtfile.readLine();
                        theArea.append( "\n" +  strLine);   
                    }
                    txtfile.close();
                }catch(FileNotFoundException e){
                    System.out.println("File Not Found");
                }catch(IOException e){
                    System.out.println("Reading Error");
                }   
                //read lines
                //put those lines in theArea - append
                //System.out.println(openChoose.getSelectedFile());
            }else{
                System.out.println("Cancelled?");
            }
        }
    }
    //Constructor
    notepadMinus(){
        theFrame = new JFrame("Notepad Minus");
        theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        thePanel = new JPanel();
        thePanel.setLayout(null);
        thePanel.setPreferredSize(new Dimension(800, 600));
        
        theBar = new JMenuBar();
        //theBar.setSize(600,50);
        //theBar.setLocation(100, 50);
        //thePanel.add(theBar);
        theFrame.setJMenuBar(theBar);
        
        theMenu = new JMenu("File");
        theBar.add(theMenu);
        
        openItem = new JMenuItem("Open");
        openItem.addActionListener(this);
        theMenu.add(openItem);
        
        saveItem = new JMenuItem("Save");
        saveItem.addActionListener(this);
        theMenu.add(saveItem);
        
        theArea = new JTextArea();
        theScroll = new JScrollPane(theArea);
        theScroll.setPreferredSize(new Dimension(800, 600));
        
        //theFrame.setContentPane(thePanel);
        theFrame.setContentPane(theScroll);
        theFrame.pack();
        theFrame.setVisible(true);
        
        openChoose = new JFileChooser();
        
    }
    //Main Method
    public static void main(String[] args){
        new notepadMinus();
    }
}

它在JTextArea中的外观

hello world
hello world
hello world
hello world
null

Answer 1

改变

theArea.append(strLine);
while(strLine != null){
    strLine = txtfile.readLine();
    theArea.append( "\n" +  strLine);   
}

到

while(strLine != null){
    theArea.append( "\n" +  strLine);   
    strLine = txtfile.readLine();
}

如果在打印前读取，您将跳过空值检查。
您已经在循环之前读取了txtfile中的一行。您应该在读取另一行之前先打印它。
这个错误还有另一个后果——第一行被跳过。如果您的文件有

a
b
c
d

作为其内容，输出将是

b
c
d
null