Java中的UDP协议常常被用来实现消息传递，不同于TCP协议的连接需要手动建立和关闭，UDP协议可随时发送和接收数据。

多线程发送数据可以提高传递速度和效率。在使用UDP协议发送数据时，我们需要创建一个DatagramSocket对象来发送和接收数据。以下是示例代码：

DatagramSocket socket = new DatagramSocket();
InetAddress receiverAddress = InetAddress.getByName("192.168.0.1");
int receiverPort = 5000;
String message = "Hello World";
byte[] sendData = message.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, receiverAddress, receiverPort);
socket.send(sendPacket);
socket.close();

对于多线程的UDP数据发送，可以创建多个线程来并发发送数据：

class SenderThread extends Thread {
private DatagramSocket socket;
private InetAddress receiverAddress;
private int receiverPort;
private String message;
public SenderThread(DatagramSocket socket, InetAddress receiverAddress, int receiverPort, String message) {
this.socket = socket;
this.receiverAddress = receiverAddress;
this.receiverPort = receiverPort;
this.message = message;
}
public void run() {
try {
byte[] sendData = message.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, receiverAddress, receiverPort);
socket.send(sendPacket);
} catch (Exception e) {
e.printStackTrace();
}
}
}
DatagramSocket socket = new DatagramSocket();
InetAddress receiverAddress = InetAddress.getByName("192.168.0.1");
int receiverPort = 5000;
String message1 = "Hello World 1";
String message2 = "Hello World 2";
String message3 = "Hello World 3";
SenderThread senderThread1 = new SenderThread(socket, receiverAddress, receiverPort, message1);
SenderThread senderThread2 = new SenderThread(socket, receiverAddress, receiverPort, message2);
SenderThread senderThread3 = new SenderThread(socket, receiverAddress, receiverPort, message3);
senderThread1.start();
senderThread2.start();
senderThread3.start();
socket.close();

在这个例子中，我们创建了三个SenderThread线程来并发发送三条消息。实际项目中可能需要更多的线程来发送数据。

多线程接收数据同样可以提高效率。下面是一个示例代码：

DatagramSocket socket = new DatagramSocket(5000);
byte[] receiveData = new byte[1024];
while (true) {
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
socket.receive(receivePacket);
String message = new String(receivePacket.getData()).trim();
System.out.println(message);
}
socket.close();

接收数据可以在一个while循环中不停地接收。在实际使用中可能需要使用其他方法来控制多线程并发接收数据。