Thread: Code doesn't work

I can't see why my code aren't working. (I'm still learning Java)
Please help me.

The Error / Console:

Exception in thread "main" java.lang.NullPointerException
	at javax.swing.ImageIcon.<init>(Unknown Source)
	at GUI_JButton.Gui.<init>(Gui.java:28)
	at GUI_JButton.Main.main(Main.java:9)

The main Class:

	public static void main(String[] args) {
 
		Gui go = new Gui();
		//This is need to close the window.
		go.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
		go.setSize(300,200);
		go.setVisible(true);
 
	}

The Gui-Class:

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
 
@SuppressWarnings("serial")
public class Gui extends JFrame{
 
	private JButton reg;
	private JButton custom;
 
	public Gui(){
		//Super is how you call methods form the SUPER-ClASS. It is also how you creat a title.
		super("The Title");
		setLayout(new FlowLayout());	//This is the default layout
 
		reg = new JButton("reg Button");
		add(reg);
 
		//This is how to import photos/icons to the buttons.
		Icon b = new ImageIcon(getClass().getResource("b.png"));
		Icon x = new ImageIcon(getClass().getResource("x.png"));
 
		//This is the cusotm button.
		custom = new JButton("Custom", b);
		custom.setRolloverIcon(x);
		add(custom);
 
		HandlerClass handler = new HandlerClass();
		reg.addActionListener(handler);
		custom.addActionListener(handler);
 
	}
 
	//When you implement a class, then you have to override all the methodes - Lucky this only has one.
	private class HandlerClass implements ActionListener{
 
		public void actionPerformed(ActionEvent e) {
			JOptionPane.showMessageDialog(null, String.format("%s", e.getActionCommand()));
		}
	}
 
}

NOTE: I' using a png-file called "b.png" and one called "x.png" - They are both in my "src" / scouce folder - Thanks for your time!

What is the problem? Are any exceptions thrown or anything?

My "program" won't run. It just shows an error.

Post the error, the whole thing.

It is the whole error... and the whole code. Just look under: "The Error / Console"

There is a null value in line 28 of the Gui class. I suspect that either or both of the files b.png and x.png are not being found. Depending on your environment setup, you may need to specify the whole path or the relative location from the source, as in "./b.png".

I tried to do this at those lines, but it didn't work.

Icon b = new ImageIcon(getClass().getResource("C:\Users\Nicklas \Dropbox\Eclipse\WorkSpace Done\Code Reminder\src\b.png"));
Icon x = new ImageIcon(getClass().getResource("C:\Users\Nicklas \Dropbox\Eclipse\WorkSpace Done\Code Reminder\src\x.png"));

The console / Error says:
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Invalid escape sequence (valid ones are \b \t \n \f \r \" \' \\ )

at GUI_JButton.Gui.<init>(Gui.java:28)
at GUI_JButton.Main.main(Main.java:9)



So i know that I did something wrong, but what? How should my code look?