TicTacToe Run-Time Error
<p>I'm currently trying to make a TicTacToe game in Java; however I've hit a roadblock I can't quite figure out. I have a function so that when the user clicks within the top left corner, it should draw and X or an O, depending on the turn - at the moment I only have it so that it should draw an O. I'm going to implement the rest once I figure the initial part out. However, when I click to draw the oval, I get an error I don't understand. My code is below, and the error will be below that.</p>

<p>P.S. I'm only a senior in high school, so I think I know what I'm doing, but I probably have no idea.</p>

<p>Main class:</p>

<pre><code>import java.awt.Color;
import javax.swing.*;


public class ticTacToeMain{

    public static void main(String[]args){
            ticTacToeBoard theBoard = new ticTacToeBoard();
            theBoard.setBackground(Color.white);
            JFrame frame = new JFrame();
            frame.add(theBoard);
            frame.setTitle("Tic Tac Toe");  
            frame.setSize(600,600);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);     
    }
}
</code></pre>

<p>Board class:</p>

<pre><code>import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class ticTacToeBoard extends JPanel{
    int turn=1;
    protected Graphics g2,g3;
    private static int x,y;

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.setColor(Color.black);
        g.drawLine(200, 0, 200, 600);
        g.drawLine(400, 0, 400, 600);
        g.drawLine(0,200, 600, 200);
        g.drawLine(0, 400, 600, 400);
        addMouseListener(new mouseListener());
    }
    public void drawX(int x1,int y1,int x2,int y2){
        g2.setColor(Color.red);
        g2.drawLine(x1, y1, x2, y2);

    }
    public void drawO(int x1, int y1, int width, int height){
        g3.setColor(Color.blue);
        g3.drawOval(x1,y1, width, height);
    }
    private class mouseListener extends MouseAdapter{
        public void mouseClicked(MouseEvent e){
            x = e.getX();
            y = e.getY();
            topLeftClicked();
        }
    }
    public void topLeftClicked(){
        if (x&lt;200 &amp;&amp; y&lt;200 &amp;&amp; turn == 0){
            drawX(25,25,175,175);
        }else if (x&lt;200 &amp;&amp; y&lt;200 &amp;&amp; turn == 1){
            drawO(25,25,150,150);
        }

    }

}
</code></pre>

<p>Here's the error:</p>

<pre><code>Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at ticTacToeBoard.drawO(ticTacToeBoard.java:34)
    at ticTacToeBoard.topLeftClicked(ticTacToeBoard.java:48)
    at ticTacToeBoard$mouseListener.mouseClicked(ticTacToeBoard.java:41)
    at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:269)
    at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:269)
    at java.awt.Component.processMouseEvent(Component.java:6528)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4542)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2750)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
</code></pre>