如何在 Applet 中为俄罗斯方块游戏设置图像

我使用小程序开发俄罗斯方块游戏.我生成了随机形状并使其移动.但我不知道如何让它沉淀在底部.一旦到达屏幕的尽头，我的形状就会消失.请在这方面帮助我.这是我的代码.

I developing tetris game using applets. I have generated random shapes and making it move. But i don't know how to make it settle at the bottom. My shapes are vanishing once it reaches the end of the screen. Please help me on this regard. Here goes my code.

import java.applet.Applet;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JLabel;



public class TetrisGame
{
    public static void main (String argsp[])
    {
        JFrame frame = new JFrame("Tetris");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final AppletClass applet = new AppletClass();
        frame.getContentPane().add(applet);
        applet.init();
        Thread t = new Thread(new Runnable()
        {

            @Override
            public void run() 
            {
                while(true)
                {
                    try 
                    {
                        Thread.sleep(1000);
                        applet.repaint();
                    }
                    catch (InterruptedException e) 
                    {
                        e.printStackTrace();
                    }               
                }
            }

        });
        t.start();

        frame.setBounds(10,10,410,610);
        frame.setVisible(true);
    }
}

class AppletClass extends Applet implements KeyListener
{

    private static final long serialVersionUID = 1L;
    static int xpos = 190;
    static int ypos =0;
    static int random1;
    static int reached_end=1;


    public void init()
    {
             System.out.println("aaa");
        setFocusable(true);
        requestFocus();
        addKeyListener(this);

    }
    public void paint (Graphics g)
    {

        generateRandomShapes(g);
    }

    public void generateRandomShapes (Graphics g)
    {

        int i=0;
        int x[] = new int[4];
        int y[] = new int[4];

        if(reached_end==1)
        {
            random1=(int)Math.floor(Math.random()*100);
            ypos=0;
        }

        x[0]=xpos;
        ypos =ypos+30;
        y[0]=ypos;

        if(ypos>420)
        {
            reached_end=1;
            ypos=0;
        }
        else
            reached_end=0;





        switch(random1%7)
        {
                case 0:
                    //straight line
                    for(i = 0;i<3;i++)
                    {
                        x[i+1]=x[i];
                        y[i+1]=y[i]+30;
                    }
                    break;
                case 1:
                    //L shape
                    for(i = 0;i<2;i++)
                    {
                        x[i+1]=x[i];
                        y[i+1]=y[i]+30;
                    }
                    x[i+1]=x[i]+30;
                    y[i+1]=y[i];
                    break;
                case 2:
                    //reverse L shape
                    for(i = 0;i<2;i++)
                    {
                        x[i+1]=x[i];
                        y[i+1]=y[i]+30;
                    }
                    x[i+1]=x[i]-30;
                    y[i+1]=y[i];
                    break;
                case 3:
                    //square shape
                    i=0;
                        x[i+1]=x[i];
                        y[i+1]=y[i]+30;
                    i++;
                        x[i+1]=x[i]+30;
                        y[i+1]=y[i];
                    i++;
                        x[i+1]=x[i];
                        y[i+1]=y[i]-30;
                    break;
                case 4:
                    //Inverse T shape
                    x[i+1]=x[i]-30;
                    y[i+1]=y[i]+30;
                    for(i = 1;i<3;i++)
                    {
                        x[i+1]=x[i]+30;
                        y[i+1]=y[i];
                    }
                    break;
                case 5:
                    //S shape
                    x[i+1]=x[i]-30;
                    y[i+1]=y[i]+30;
                    i++;
                    x[i+1]=x[i]+30;
                    y[i+1]=y[i];
                    i++;
                    x[i+1]=x[i]+30;
                    y[i+1]=y[i]-30;
                    break;
                case 6:
                    //Z shape
                    x[i+1]=x[i]+30;
                    y[i+1]=y[i];
                    i++;
                    x[i+1]=x[i];
                    y[i+1]=y[i]+30;
                    i++;
                    x[i+1]=x[i]+30;
                    y[i+1]=y[i];
                    break;

        }
        g.setColor(Color.BLACK);
        for(i=0;i<4;i++)
        {
            g.fillRect(x[i], y[i], 30, 30);
        }


    }

    public void keyReleased(KeyEvent e){;}
     public void keyTyped(KeyEvent e){;}

    public void keyPressed(KeyEvent e) 
    {
        System.out.println("Kkk "+e.getKeyCode());
        if(e.getKeyCode() == KeyEvent.VK_LEFT)
     {
        if(xpos>=30)
        {
            xpos=xpos-30;
        }
        System.out.println("xpos is :" + xpos);
     }
     if(e.getKeyCode() == KeyEvent.VK_RIGHT)
     { 
         xpos=xpos+30;
     }

     if(e.getKeyCode() == KeyEvent.VK_DOWN || e.getKeyCode() == KeyEvent.VK_SPACE)
     {
         ypos=420;
     }
 }
}

TIA