用箭头键移动矩形

Question

Basically, I am trying to make a program that moves a "platter" one pixel to the left when the left arrow key is pressed, and one to the right when the right arrow key is pressed. Currently, nothing is drawing on my output window when I compile and run, and I am not too sure what I am doing wrong here or where exactly the code isn't doing what I want. Any help is appreciated, thank you!

import java.awt.*;
import java.net.*;
import java.util.*;
import java.applet.Applet;


public class game extends Applet
{
    Thread loopThread;
    boolean left  = false;
    boolean right = false;
    int platPos = 50;

    public void run() 
    { 
        Graphics g = null;

        int i, j;
        long startTime;



        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
        startTime = System.currentTimeMillis();

        while (Thread.currentThread() == loopThread) 
        {
            updatePlatter(g);
        }
    }


     public void updatePlatter(Graphics g) 
    {

         if(left)
         {
             g.setColor(new Color(255,255,255));
             g.fillRect(50+platPos, 200, 100, 20);
             platPos--;
             g.setColor(new Color(100,100,100));
             g.fillRect(50+platPos,200, 100,20);
         }

         if(right)
         {
             g.setColor(new Color(255,255,255));
             g.fillRect(50+platPos,200,100,20);
             platPos++;
             g.setColor(new Color(100,100,100));
             g.fillRect(50+platPos,200,100,20);
         }

    }

    public boolean keyDown(Event e, int key) 
    {
      if (key == Event.LEFT)
        left = true;

      if (key == Event.RIGHT)
        right = true;
      return true;
    }
}

Answer 1

I deleted my answer as it's impossible to fix your existing code without rewriting everything, here is a good starting point for you to learn :

http://www.cs.stir.ac.uk/~sbj/examples/Java-examples-basic/Move/Move.java

Basically it does what you want but using buttons.

Also as @Ben stated, you should consider using something else than Applet, it's pretty dead..