Question

此课程Time：

public class Time {

  int secondPassed = 0;
  Timer mytime = new Timer()

  TimerTask mytask = new TimerTask() {
    public void run()  {
      secondPassed++;

      if(secondPassed == 3) {
        secondPassed = 0;

         Udp callUdp = new Udp();
         String trnsferRP = callUdp.trnsfrRPckt();
         System.out.println(trnsferRP + "exp");
         System.out.println("Its 10");
      }
       else {
         System.out.println("Second : " + secondPassed);
      }
    }
  };

  public void start(){
    mytime.scheduleAtFixedRate(mytask, 1000,1000);
  }

  public static void main(String[] args) throws Exception {
    Time starter = new Time();
    starter.start();
  }
}

这是课程UDP：

public class Udp {

  public DatagramPacket receivePacket;
  public String result;

  public void socketp() throws Exception {
    DatagramSocket clientSocket = new DatagramSocket(10076);
    InetAddress IPAddress = InetAddress.getByName("192.168.100.10");
    byte[] sendData = new byte[9];
    byte[] receiveData = new byte[9];
    String sentence = "VDV2bE1";
    sendData = sentence.getBytes();
    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 10076);
    clientSocket.send(sendPacket);
    this.receivePacket = new DatagramPacket(receiveData, receiveData.length);
    clientSocket.receive(receivePacket);
    clientSocket.close();
    this.result = new String(receivePacket.getData());
    return;
  }

  public String trnsfrRPckt(){
    return this.result;
  }
}

因此，我尝试将class Udp中的变量调用到class Time，因为我想要打印收到的数据包。目前我的结果是：

second : 1
second : 2
nullexp
its 10

为什么null出来了？应该是分组数据+＆＃34; exp＆＃34;

Answer 1

你从未打过电话

callUdp.socketp();

哪个是写入结果变量的唯一函数。因此，在调用socketp（）之前，结果为null。

从另一个类打印变量？

1 个答案: