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randint

Sun Aug 07, 2011 11:03 pm


NullPointerException

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For whatever reason, there is a NullPointerException in a GUI Program I made to open files:
[code]
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
public class ReadWriteFile extends JFrame implements ActionListener 
{
	public JFrame f1 = new JFrame("Open/Save");
	public JFrame f2 = new JFrame("Choose file");
	public JPanel p1 = new JPanel();
	public JPanel p2 = new JPanel();
	public JButton b1 = new JButton ("Open");
	public JButton b2 = new JButton ("Save");
	public JFileChooser fc = new JFileChooser();
	public File f;
	public int select;
	public ReadWriteFile()
	{
		f1.setContentPane(p1);
		f1.setSize(300, 300);
		f1.setResizable(true);
		p1.add(b1);
		p1.add(b2);
		f2.setContentPane(p2);
		f2.setSize(500, 500);
		f2.setResizable(true);
		p2.add(fc);
		b1.addActionListener(this);
		b2.addActionListener(this);
		f1.setVisible(true);
	}
	public void actionPerformed(ActionEvent e)
	{
		if (e.getSource() == b1)
		{
			f2.setVisible(true);
			FileRead();
		}
	}
	public void FileRead()
	{
		if (select == fc.APPROVE_OPTION)
		{
			f = fc.getSelectedFile();
		}
	}
	public static void main(String args[]) throws Exception
	{
		ReadWriteFile rwf = new ReadWriteFile();
	}
}
[/code]
The java.lang.NullPointerException occurs when the user attempts to open a file, I do not know why this is.[/list]


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Tony

Sun Aug 07, 2011 11:47 pm


RE:NullPointerException

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Because, on the line where this exception is thrown, you are trying to call a method on NULL. Try to step backwards to figure out why that variable did not have any value assigned to it.