Java-JFrame保存多行

Question

I've been banging my head against the wall last couple of hours trying to get my program to work, but to no success.

I'm working on a simple JFrame based program that should open the window, let me input the variables and then if I press Save, save them to selected .csv file.

The problem however arises when I try to save 2 or more sets of variables, the first one always gets overwritten and only new one is there.

For example instead of:

Mark, 100, 2, John, 50, 1

In the file I only find

John 50, 1

I'm guessing it has to do with new bufferedwriter being created every time I click 'Save' button but I have no idea how to get around doing that, I tried multiple positions of placing it but it never works because I get error if it's outside the Action method.

Here's the code:

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

/**
 * Demonstrates etc
 */
public class Homework1 extends JFrame implements ActionListener {

   JTextField jtfName1;
   JTextField jtfName2;
   JTextField jtfName3;
   JTextField jtfName4;

   static File file = new File("121Lab1.csv"); 

   public Homework1() {
        // Set BorderLayout with horizontal gap 5 and vertical gap 10
      setLayout(new BorderLayout(10, 10));


        // Create a JPanel with FlowLayout for the South of the JFrame's BorderLayout

      JPanel jpSouth = new JPanel(new FlowLayout(FlowLayout.CENTER, 20, 3));

        // Create some buttons to place in the south area
      JButton jbCalc = new JButton("Calculate");
      JButton jbSave = new JButton("Save");
      JButton jbClear = new JButton("Clear");
      JButton jbExit = new JButton("Exit");

      jpSouth.add(jbCalc);
      jpSouth.add(jbSave);
      jpSouth.add(jbClear);
      jpSouth.add(jbExit);

      jbCalc.addActionListener(this);
      jbSave.addActionListener(this);
      jbClear.addActionListener(this);
      jbExit.addActionListener(this);


        // Place the south panel in the JFrame's south area
      add(jpSouth, BorderLayout.SOUTH);

        // Add textfields to the rest of the frame

      JPanel jpCenter = new JPanel(new GridLayout(0,2));

      jpCenter.add(new JLabel("Item name: ", SwingConstants.RIGHT));
      jtfName1 = new JTextField("", 10);
      jpCenter.add(jtfName1);
      jtfName1.addActionListener(this);

      jpCenter.add(new JLabel("Number of: ", SwingConstants.RIGHT));
      jtfName2 = new JTextField("", 10);
      jpCenter.add(jtfName2);
      jtfName2.addActionListener(this);

      jpCenter.add(new JLabel("Cost: ", SwingConstants.RIGHT));
      jtfName3 = new JTextField("", 10);
      jpCenter.add(jtfName3);
      jtfName3.addActionListener(this);

      jpCenter.add(new JLabel("Amount owed: ", SwingConstants.RIGHT));
      jtfName4 = new JTextField("", 10);
      jpCenter.add(jtfName4);
      jtfName4.addActionListener(this);

      add(jpCenter, BorderLayout.CENTER);

   }

   public void actionPerformed(ActionEvent ae) {
      String actionString = ae.getActionCommand(); // gets the string on the component
      Object actionObj = ae.getSource();


      if (actionString.equalsIgnoreCase("Calculate")) { // ae.getSource() == jbCancel
         System.out.println("You clicked Calculate");
         try {
            double value = Double.parseDouble(jtfName2.getText())*Double.parseDouble(jtfName3.getText());
            jtfName4.setText(String.format("%.2f", value));
         } 
         catch (NumberFormatException nfe) {
            jtfName4.setText("Not a number");
         }

      } 
      else if (actionString.equalsIgnoreCase("Save")) { 

         try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(file));
            writer.write(jtfName1.getText()+",");
            writer.write(jtfName2.getText()+",");
            writer.write(jtfName3.getText()+"\r\n");
            writer.flush();
            writer.close();
         } 
         catch(IOException e) {
            System.out.println("IO Error");
         }         
      } 
      else if (actionString.equalsIgnoreCase("Clear")) { 

         System.out.println("You clicked Clear");
         jtfName1.setText("");
         jtfName2.setText("");
         jtfName3.setText("");
         jtfName4.setText("");

      } 
      else if (actionString.equalsIgnoreCase("Exit")) { 


         setVisible(false);
         dispose();


      } 
      else {
         System.out.println("Unknown command: " + actionString);
         System.out.println("Unknown source:  " + actionObj);
      }
   } 




   public static void main(String[] args) throws IOException {

      Homework1 jfMain = new Homework1();
      jfMain.setTitle("Item Order Calculator");
      jfMain.setSize(450, 200);
      jfMain.setLocationRelativeTo(null);       // Center JFrame
      jfMain.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      jfMain.setVisible(true);


   } // end main
} // end class JPanelTester

Answer 1

Each time you click save , the file and it's contents are been overwritten. You need to tell the FileWriter that you wish to append to the end of the file, for example...

BufferedWriter writer = new BufferedWriter(new FileWriter(file), true);

See FileWriter(File, boolean) for more details

BufferedWriter also has a newLine method, which can write a new line to the file...

writer.write(jtfName1.getText()+",");
writer.write(jtfName2.getText()+",");
writer.write(jtfName3.getText());
writer.newLine();

You're also not managing your resources very well. If you open a resource, you should make every attempt to close it, otherwise you could end up with leaking resources and other strange problems

Luckily in Java 7+, it's very easy to manage these types of resources

    try (BufferedWriter writer = new BufferedWriter(new FileWriter(file))) {
        writer.write(jtfName1.getText()+",");
        writer.write(jtfName2.getText()+",");
        writer.write(jtfName3.getText());
        writer.newLine();
     } 
     catch(IOException e) {
        System.out.println("IO Error");
     }       

See The try-with-resources Statement for more details

Answer 2

您可以在启动时清除/删除文件并附加到文件中，如下所示： 如何在Java中将文本附加到现有文件中

Answer 3

i will suggest you one other writer(i have worked on this):

try{ 

 PrintWriter Writer = new PrintWriter(new File("path of file/file.(whatever)");

    //example
        writer.write(jtfName1.getText()+",");
        writer.printf("  "); //Leave some space
        writer.write(jtfName2.getText()+",");
        writer.printf("  "); //Leave some space
        writer.write(jtfName3.getText()+"\r\n");
        writer.printf("  "); //Leave some space

        writer.flush();
        writer.close();

} catch (FileNotFoundException e) { e.printStackTrace(); }

if you want to leave some space or write something use: writer.printf(".");

if you want to leave a line use writer.println();

Of course it has and other fuctions to use with this writer..

Let me know if it does your job.....