Problem with Formatters (I think)

[sindreb]

Hi!
I'm trying to make a program with gui. The window should have 2 textfields and one button. One of the textfield are uneditable. When the button is clicked i want the stuff from the first textfield to be written to a file and I want the second textfield to output the text from the file. The gui works fine, but whenever I press the button i get a bunch of errors. This is the code I'm using:

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.*;
 
public class GUI extends JFrame{
	private JTextField toFile;
	private JTextField fromFile;
	private JButton sendToFile;
	private FileHandling fh;
 
	public GUI(){
	super("File");
	setLayout(new FlowLayout());
 
	toFile = new JTextField("Write what you want to send to the file",20);
	add(toFile);
 
	sendToFile=new JButton("Add to file");
	add (sendToFile);
 
	fh=new FileHandling();
	fh.checkFile();
	fh.readFile();
 
	fromFile=new JTextField(fh.fromFile,20);
	fromFile.setEditable(false);
	add(fromFile);
 
	HandlerClass hc=new HandlerClass();
	sendToFile.addActionListener(hc);
}
	private class HandlerClass implements ActionListener{
		public void actionPerformed(ActionEvent event){
			String a=fromFile.getText();
			fh.writeFile(a);
		}
	}
}

import java.io.*;
import java.util.*;
 
public class FileHandling {
	private Formatter x;
	private Scanner s;
	private File y;
	public String fromFile;
 
	public void checkFile(){
		y=new File("data.txt");
		if(y.exists()){
			try{
				s=new Scanner(y);
			}
			catch(Exception e){
				System.out.println("Could not scan the file");
			}
		}else{
			try{
				x=new Formatter("data.txt");
				s=new Scanner(y);
			}
			catch(Exception e){
				System.out.println("Could not create the file");
			}
		}
	}
	public void readFile(){
		while(s.hasNextLine()){
			fromFile=s.nextLine();
		}
	}
	public void writeFile(String a){
		x.format("%s \n", a);
	}
	public void closeFile(){
		x.close();
	}
}

If anyone can tell me what I'm doing wrong I would be very grateful.

[Junky]

Do you think that posting the error messages might help?

[sindreb]

Do you think that posting the error messages might help?

Sure
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at FileHandling.writeFile(FileHandling.java:35)
at GUI$HandlerClass.actionPerformed(GUI.java:37)
at javax.swing.AbstractButton.fireActionPerformed(Unk nown Source)
at javax.swing.AbstractButton$Handler.actionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)

The problem is that these are just half of the error messages I get.

[copeg]

A NullPointerException means something is null. What is null on line 35 of the FileHandling class? What variables do you access on that line? Add some println's to see. Once you determine what is null, backtrack through the code to determine why it was never initialized and determine the most appropriate way to initialize.

[sindreb]

Thanks! Found out I never initialized the Formatter if the file did'nt exist. Now my problem is that the second textfield, fromFile, does not display anything. Any clue on how I can fix that?

[copeg]

Thanks! Found out I never initialized the Formatter if the file did'nt exist. Now my problem is that the second textfield, fromFile, does not display anything. Any clue on how I can fix that?

Do you ever set the text of the JTextField?

[sindreb]

Do you ever set the text of the JTextField?

Yeah, it is automaticly filled with "Write what you want to send to the file". I also checked a bit, and the file data.txt is being created, but it never gets any data. I also tried to put some text in the file, but it did not show up in the second textfield. I have really no idea why it does not work :/

[Junky]

If you have no content in the output file the most common mistake is not closing the Writer.

[sindreb]

So, how do I close the writer? I'm sorry, but I'm kinda new to java

[Junky]

Did you bother to read the API to see what methods the class has?