Java 按下jButton时如何将数据追加到文件中
我一直在创建一个GUI应用程序,为学生注册数据,数据填写在提供的JTextfields中。按下submit按钮后,我将其编程为以我喜欢的某种方式(安排)将数据存储到文件中。对于第一次提交,程序运行良好,并将数据存储到文件中,但在其他连续的Java 按下jButton时如何将数据追加到文件中,java,Java,我一直在创建一个GUI应用程序,为学生注册数据,数据填写在提供的JTextfields中。按下submit按钮后,我将其编程为以我喜欢的某种方式(安排)将数据存储到文件中。对于第一次提交,程序运行良好,并将数据存储到文件中,但在其他连续的提交中,在此处输入代码(即当学生重新填写时),程序要么覆盖,要么根本不写入文件中。以下是迄今为止的代码: import javax.swing.*; import java.awt.*; import java.awt.event.ActionEvent; im
提交中,在此处输入代码(即当学生重新填写时),程序要么覆盖,要么根本不写入文件中。以下是迄今为止的代码:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintStream;
public class StudentAssignment extends JFrame {
private JLabel lblFname, lblbSname, lblRegNo, lblPos;
private JButton btnsubmit;
private JTextField txtFname, txtSname, txtRegNo, txtPos;
private JPanel panel1, panel12, panel3, panel4,panel5;
private int i = 1;
private File myFile;
private FileWriter fw;
private PrintStream ps;
public StudentAssignment() throws Exception{
componentInitialization();
setVisible(true);
myFile =new File("Mustard.txt");
fw = new FileWriter(myFile,true);
ps = new PrintStream(myFile);
actionListeners();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void componentInitialization(){
setBounds(200, 200, 300, 300);
setTitle("Mustard's Frame");
setLayout(new GridLayout(5,1));
lblFname = new JLabel("First Name");
txtFname = new JTextField(10);
panel1 = new JPanel();
panel1.add(lblFname); panel1.add(txtFname);
lblbSname = new JLabel("Surname");
txtSname = new JTextField(10);
panel12 = new JPanel();
panel12.add(lblbSname); panel12.add(txtSname);
lblRegNo = new JLabel("Registration Number");
txtRegNo = new JTextField(10);
panel3 = new JPanel();
panel3.add(lblRegNo); panel3.add(txtRegNo);
lblPos = new JLabel("program of study");
txtPos = new JTextField(10);
panel4 = new JPanel();
panel4.add(lblPos); panel4.add(txtPos);
btnsubmit = new JButton("SUBMIT");
panel5 = new JPanel();
panel5.add(btnsubmit);
add(panel1); add(panel12);
add(panel3); add(panel4);
add(panel5);
}
public void actionListeners(){
btnsubmit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
fileStoring();
}catch (Exception exc){
}
clearFields();
}
});
}
public void fileStoring() throws Exception{
System.setOut(ps);
System.out.printf("%-10s %-15s %-15s %-15s %-15s\n", "Sno.", "First Name", "Surname", "Reg.No", "Program of Study");
System.out.printf("%-10d %-15s %-15s %-15s %-15s\n",i,txtFname.getText(), txtSname.getText(), txtRegNo.getText(), txtPos.getText() );
i++;
fw.close();
ps.close();
}
public void clearFields(){
txtFname.setText("");
txtSname.setText("");
txtRegNo.setText("");
txtPos.setText("");
txtFname.requestFocus();
}
public static void main(String[] args) throws Exception{
StudentAssignment obj = new StudentAssignment();
}
}
像这样改变你的方法
public void fileStoring() throws Exception {
try (FileWriter fileWriter = new FileWriter("C:\\data\\Mustard.txt", true);
PrintWriter printWriter = new PrintWriter(fileWriter)) {
if (i == 1) {
printWriter.printf("%-10s %-15s %-15s %-15s %-15s\n", "Sno.", "First Name", "Surname", "Reg.No",
"Program of Study");
}
printWriter.printf("%-10d %-15s %-15s %-15s %-15s\n", i, txtFname.getText(), txtSname.getText(),
txtRegNo.getText(), txtPos.getText()).toString();
} catch (IOException e) {
// handle the exception here.
}
i++;
}
没有得到所需结果的原因是在构造函数中初始化流,然后在第一次写入后关闭流
fw.close();
ps.close();
随后的写入将失败。为了解决这个问题,您需要在每次写入文件时创建一个新流(即,在这个方法本身内部,而不是在构造函数内部),然后关闭它。还请注意,您只需要在开始时编写头文件,而您的实现也无法处理此问题。它已经成功运行,我非常感谢您的贡献
以下是根据您的建议编辑的代码:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.*;
public class StudentAssignment extends JFrame {
private JLabel lblFname, lblbSname, lblRegNo, lblPos;
private JButton btnsubmit;
private JTextField txtFname, txtSname, txtRegNo, txtPos;
private JPanel panel1, panel12, panel3, panel4,panel5;
private int i = 1;
public StudentAssignment() throws Exception{
componentInitialization();
setVisible(true);
actionListeners();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void componentInitialization(){
setBounds(200, 200, 300, 300);
setTitle("Mustard's Frame");
setLayout(new GridLayout(5,1));
lblFname = new JLabel("First Name");
txtFname = new JTextField(10);
panel1 = new JPanel();
panel1.add(lblFname); panel1.add(txtFname);
lblbSname = new JLabel("Surname");
txtSname = new JTextField(10);
panel12 = new JPanel();
panel12.add(lblbSname); panel12.add(txtSname);
lblRegNo = new JLabel("Registration Number");
txtRegNo = new JTextField(10);
panel3 = new JPanel();
panel3.add(lblRegNo); panel3.add(txtRegNo);
lblPos = new JLabel("program of study");
txtPos = new JTextField(10);
panel4 = new JPanel();
panel4.add(lblPos); panel4.add(txtPos);
btnsubmit = new JButton("SUBMIT");
panel5 = new JPanel();
panel5.add(btnsubmit);
add(panel1); add(panel12);
add(panel3); add(panel4);
add(panel5);
}
public void actionListeners(){
btnsubmit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
try {
fileStoring();
}catch (Exception exc){
}
clearFields();
}
});
}
public void fileStoring() throws Exception {
try (FileWriter fileWriter = new FileWriter("Mustard.txt", true);
PrintWriter printWriter = new PrintWriter(fileWriter)) {
if (i == 1) {
printWriter.printf("%-10s %-15s %-15s %-15s %-15s\n", "Sno.", "First Name", "Surname", "Reg.No",
"Program of Study");
}
printWriter.printf("%-10d %-15s %-15s %-15s %-15s\n", i, txtFname.getText(), txtSname.getText(),
txtRegNo.getText(), txtPos.getText()).toString();
} catch (IOException e) {
}
i++;
}
public void clearFields(){
txtFname.setText("");
txtSname.setText("");
txtRegNo.setText("");
txtPos.setText("");
txtFname.requestFocus();
}
public static void main(String[] args) throws Exception{
StudentAssignment obj = new StudentAssignment();
}
}为什么要使用系统放样(ps)代码>?您有一个打印流
,直接使用即可。在写入文件之前,您还需要重新打开该文件。您真的应该看看Try moving fw=new FileWriter(myFile,true);ps=新的打印流(myFile);到fileStoring()方法的开头。这可能是因为如果你每次使用它们时都重新实例化它们,那么你就关闭了它们work@MadProgrammersetout(ps)将以下代码的整行写入一个文件中(我从某个YouTube来源了解到)。因此,我打算将这两个Sys.out.printf(//代码)写入行中,它在第一次单击按钮时就成功了,但在其他连续的按钮单击时就不起作用了。但无论如何,您标记的资源非常有用。@Abdul razaqTwahaSystem.setout(ps)
将您的标准输出流(您用于打印到屏幕上的内容)替换为指定的PrintStream
,这在最好的情况下是不可取的,但是由于PrintStream
具有与System.out.println
相同的功能,这似乎是一种浪费精力和毫无意义的练习,只会破坏将打印语句输出到控制台的可能性,而控制台可用于向用户提供调试信息或提示,但由于您关闭了底层流,它只会破坏底层流API@JRowan我尝试移动它,但问题仍然存在,它现在增加了迭代次数(I++),但数据没有更新。我不应该关闭溪流吗?(数据仅在第一次提交时更新,但在其他提交时未更新)您提供的代码已按我的要求成功运行。我非常感谢您的帮助,先生。@Abdul razaqTwaha您可以投赞成票和/或将其标记为答案,也可以投反对票。这就是我们在这里的做法。仅供参考。