I'm writing java code for a class and I get this error when I try to run the code. 
The Error Message is 

```
"Exception in thread "main" java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(Unknown Source)
at MemoControl.<init>(MemoControl.java:27)
at MemoControl.main(MemoControl.java:76)"

```

The assignment was to

"Write a graphical version of a card matching game using Swing. Your program should have 4 rows and 5 columns of "cards" that are blank on one side and have a number on the other. The game is played by clicking on two cards which are turned over. If they match, they stay visible. If they don't, they are flipped back face down. Your program should have a "Continue" button which flips back two unmatching cards and a timer that displays the number of seconds since the game started."

```
import java.awt.*;
import javax.swing.*;
import javax.swing.JFrame;
import java.awt.event.*;

public class MemoControl extends JFrame {

public JLabel label;
public JButton button;

// images
public ImageIcon image1;
public JLabel label1;
public ImageIcon image2;
public JLabel label2;
public ImageIcon image3;
public JLabel label3;
public ImageIcon image4;
public JLabel label4;
public ImageIcon image5;
public JLabel label5;

public MemoControl() {

    setLayout(new FlowLayout());

    image1 = new ImageIcon(getClass().getResource("card_cover1.jpg"));
    label1 = new JLabel(image1);
    add(label1);

    image2 = new ImageIcon(getClass().getResource("card_cover1.jpg"));
    label2 = new JLabel(image2);
    add(label2);

    image3 = new ImageIcon(getClass().getResource("card_cover1.jpg"));
    label3 = new JLabel(image3);
    add(label3);

    image4 = new ImageIcon(getClass().getResource("card_cover1.jpg"));
    label4 = new JLabel(image4);
    add(label4);

    image5 = new ImageIcon(getClass().getResource("card_cover1.jpg"));
    label5 = new JLabel(image5);
    add(label5);

    /*
     * label = new JLabel("Welcome to AMY Memo Game"); add(label);
     */

    /*
     * textField = new JTextField(15); add(textField);
     */

    button = new JButton("Flip");
    add(button);

    EventClass event = new EventClass();
    button.addActionListener(event);

}// MyMemo constr end

private class EventClass implements ActionListener {

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == button) {
            image1 = new ImageIcon(getClass().getResource("deer_card.jpg"));
            label1 = new JLabel(image1);
        }

    }
}// Event class end

public static void main(String args[]) {

    MemoControl gui = new MemoControl();

    gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    gui.pack();
    gui.setVisible(true);
    gui.setTitle("My Memo");

}// main end

}// AMYMemo class end

```