Java - Cannot find symbol?

Question

I've practicing a little here but I just can't figure it out. I declared the ArrayList ns but it cannot be found: error: cannot find symbol ns.Add(aa); Why? Sure that I simply don't see something obvious.

import javax.swing.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import java.util.Random;
import java.util.*;
import java.io.*;


public class Pixels6 extends JFrame
{   
static java.util.List ns = new ArrayList();


class PaintingComponent extends JPanel
{
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        setBackground(Color.black);
    } 
} 

public static void main( String[] args ) throws InterruptedException, IOException

{ 
    try
    {
            fl = new FileInputStream("test_for_java2.s8");
            aa = fl.read(); 

    javax.swing.Timer swTimer = new javax.swing.Timer( 10, new ActionListener()
    {
        public void actionPerformed(ActionEvent ae)
        {               
            if (aa!=-1)
            {
                aa -= 128;  
                aa = -aa; 
                ns.Add(aa);
                try 
                    {aa=fl.read(); }    
                catch( IOException e )
                {   
                    System.out.println( "Access denied: " + e );
                    System.out.println( e );
                }  
            }
            else    try 
                    {fl.close();} 
                catch( IOException e )
                {
                    System.out.println( "Access denied: " + e );
                    System.out.println( e );
                } 
        } /// Action

    }); /// Timer
    swTimer.start();

    } //try

    catch( IOException e )
        {
            System.out.println( "Access denied: " + e );
            System.out.println( e );
        }


    SwingUtilities.invokeLater( new Runnable()
    {
        public void run()
        {
            new Pixels6().setVisible(true);
        }
    });

} /// main

} /// Pixels6 extends JFrame

Answer 1

change to

ns.add(aa);  //not ns.Add(aa);

java is case sensitive language