怎样把java应用 变为一个apk

我弄了一个android socket 
public class AndroidServer implements Runnable{
public void run() {
  try {
   ServerSocket serverSocket=new ServerSocket(54321);
   while(true)
   {
    System.out.println("等待接收用户连接：");
    //接受客户端请求
    Socket client=serverSocket.accept();
    try
    {
     //接受客户端信息
     BufferedReader in=new BufferedReader(new InputStreamReader(client.getInputStream()));
     String str=in.readLine();
     System.out.println("read:  "+str);
     //向服务器发送消息
     PrintWriter out=new PrintWriter(new BufferedWriter(new OutputStreamWriter(client.getOutputStream())),true);
     out.println("return "+str);
     in.close();
     out.close();
    }catch(Exception ex)
    {
     System.out.println(ex.getMessage());
     ex.printStackTrace();
    }
    finally
    {
     client.close();
     System.out.println("close");
    }
   }
  } catch (IOException e) {
   System.out.println(e.getMessage());
  }
}
public static void main(String [] args)
{
  Thread desktopServerThread=new Thread(new AndroidServer());
  desktopServerThread.start();
}
}
怎样把以上代码最终写成apk的