troubleshooting Question

NullPointException error don't see it

Avatar of Drop_of_Rain
Drop_of_Rain asked on
Java
22 Comments2 Solutions241 ViewsLast Modified:
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class MyClass4 extends JPanel {  //starts class
        JPanel jPanel;
        ArrayList myArrayList = new ArrayList();

    // Constructor
    public MyClass4() { //starts constructor
       
        setLayout(new GridLayout(0,3)); // Setting MY layout...
         looprow:
    for (int row=0; row<20; row++) {
    for(int col=0; col<3; col++) {
    int n=(20*col+row+1);
    if (n>50) break looprow;
    JCheckBox check = new JCheckBox("" + n);
    myArrayList.add(check);
    add(check); // Adding it to ME

        jPanel.addMouseListener(new MouseAdapter() {
            public void mouseEntered(MouseEvent e) {
                jPanel.setBackground(Color.blue);
                }
                public void mouseClicked(MouseEvent e) {
                    jPanel.setBackground(Color.red);
                    }
                    public void mouseExited(MouseEvent e) {
                        jPanel.setBackground(Color.white);
                        }
                        });
}
}
    }//ends constructor
}// ends class
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