InputStreams和OutputStreams

Question

我寫了這個簡短的程序，它有一個小GUI。它應該允許你輸入文本，然後你可以將它保存到一個txt文件或從先前保存的文件讀取或刪除一個現有的文件。 它的工作原理，但有一些奇怪的錯誤。有時在創建文件後，如果我嘗試刪除它，它將不會刪除該文件。

另外，我完全不知道我是否以良好的方式編寫代碼。 我在想，如果你能看看我寫的東西，並發現我應該用不同的方式編寫的弱點或區域。也許你可以看到爲什麼在創建文件後刪除文件時出現問題。我真的很茫然，我不知道該問誰。 這裏是我的代碼：

public class InputOutout extends JFrame{ 

    private static final long serialVersionUID = -7073762217756427192L; 

    JLabel label; 
    JTextField tf; 
    JButton buttonAdd; 
    JButton buttonDisplay; 
    JButton buttonErase; 

    public InputOutout() { 
     try { 
      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 

     setLayout(new FlowLayout()); 

     label = new JLabel("Enter text"); 
     add(label); 

     tf = new JTextField(10); 
     add(tf); 

     buttonAdd = new JButton("Press to save to file"); 
     add(buttonAdd); 

     buttonDisplay = new JButton("Press to display file content"); 
     add(buttonDisplay); 

     buttonErase = new JButton("Press to erase file"); 
     add(buttonErase); 

     eventAdd add = new eventAdd(); 
     eventDisplay remove = new eventDisplay(); 
     eventErase erase = new eventErase(); 

     buttonAdd.addActionListener(add); 
     buttonDisplay.addActionListener(remove); 
     buttonErase.addActionListener(erase);  
    } 

    private class eventAdd implements ActionListener { 

     public void actionPerformed(ActionEvent e) { 
      try { 
       String word = tf.getText()+ " "; 
       FileWriter stream = new FileWriter("text.txt",true); 
       BufferedWriter out = new BufferedWriter(stream); 
       out.append(word); 
       out.close(); 
       tf.setText(""); 
      } catch (Exception ex){ 
       JOptionPane.showMessageDialog(null,ex.getMessage()); 
      } 

     } 
    } 

    private class eventDisplay implements ActionListener { 

     public void actionPerformed(ActionEvent e) { 
      try { 
       FileReader stream = new FileReader("text.txt"); 
       BufferedReader in = new BufferedReader(stream); 
       String text = in.readLine(); 
       JOptionPane.showMessageDialog(null, text); 
       stream.close(); 
      } catch (Exception ex){ 
       JOptionPane.showMessageDialog(null,ex.getMessage()); 
      } 

     } 
    } 

    private class eventErase implements ActionListener { 

     public void actionPerformed(ActionEvent e) { 
      try { 
       File file = new File("text.txt"); 
       boolean success = file.delete(); 

       if (!success) { 
        JOptionPane.showMessageDialog(null, "File was not deleted"); 
       } else { 
        JOptionPane.showMessageDialog(null, "File was deleted"); 
       } 
      } catch (Exception ex) { 
       JOptionPane.showMessageDialog(null,ex.getMessage()); 
      } 
     } 
    } 

    public static void main(String[] args) { 

     InputOutout gui = new InputOutout(); 

     gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     gui.setSize(350,100); 
     gui.setTitle("SuperWORD 2013"); 
     gui.setVisible(true);  
    } 
} 

Answer 1

圍繞file.delete()邏輯是不太正確的，因爲如果它被刪除true纔會返回。這意味着file.delete()將返回false如果它不存在。檢查文件是否存在試圖刪除它之前：

File file = new File("text.txt"); 
if (file.exists()) 
{ 
    if (!file.delete()) 
    { 
     JOptionPane.showMessageDialog(null, "File was not deleted"); 
    } 
    else 
    { 
     JOptionPane.showMessageDialog(null, "File was deleted"); 
    } 
} 
else 
{ 
    JOptionPane.showMessageDialog(null, "File does not exist"); 
} 

建議使用try {} catch() finally {}結構，以確保BufferedReader.close()，或BufferedWriter.close()被稱爲：

try 
{ 
    BufferedWriter out = new BufferedWriter(new FileWriter("text.txt",true)); 
    try 
    { 
     String word = tf.getText()+ " "; 
     out.append(word); 
     tf.setText(""); 
    } 
    finally 
    { 
     try 
     { 
      out.close(); 
     } 
     catch (IOException ex) 
     { 
      // Report close failure. 
      JOptionPane.showMessageDialog(null, ex.getMessage()); 
     } 
    } 
} 
catch (Exception ex) 
{ 
    // Report open or write failure. 
    JOptionPane.showMessageDialog(null,ex.getMessage()); 
}