InputStreams和OutputStreams

Question

我寫了這個簡短的程序，它有一個很小的GUI。 它應該允許您鍵入文本，然后您可以將其保存為txt文件或從以前保存的文件中讀取或刪除現有文件。 它有效，但有一些奇怪的錯誤。 有時在創建文件后，如果我嘗試刪除它，它將不會刪除該文件。

另外，我完全不確定我是否以良好的方式編寫代碼。 我想知道你是否可以看看我寫的東西，發現我應該寫不同的弱點或區域。 也許你可以看到為什么在創建文件后刪除文件有問題。 我真的很茫然，我不知道該問誰。 這是我的代碼：

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

file.delete()周圍的邏輯不太正確，因為只有刪除它才會返回true 。 這意味着如果file.delete()不存在，它將返回false 。 在嘗試刪除文件之前檢查文件是否存在：

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 {}構造來確保調用BufferedReader.close()或BufferedWriter.close() ：

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());
}