按照老师的代码写在本地运行报错的问题

报错内容
15:39:54: Executing task 'UdpServer.main()'...

Executing tasks: [UdpServer.main()] in project F:\AndoridProject\Socket\Socket_https


FAILURE: Build failed with an exception.

* Where:
Initialization script 'C:\Users\31851\AppData\Local\Temp\UdpServer_main__.gradle' line: 20

* What went wrong:
A problem occurred configuring project ':app'.
> Could not create task ':app:UdpServer.main()'.
   > SourceSet with name 'main' not found.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.4.1/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 1s
15:39:57: Task execution finished 'UdpServer.main()'.

服务端代码：

package com.example.socket_https.udp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Scanner;

/**
 * @author 31851
 */
public class UdpServer {
    private InetAddress mInetAddres;
    private int mPort = 7777;
    private DatagramSocket mSocket;
    private Scanner mScanner;

    public UdpServer(){
        try {
            //获取本地地址
            mInetAddres = InetAddress.getLocalHost();
            mSocket = new DatagramSocket(mPort,mInetAddres);

            //System.out.println("服务端发消息：");
            mScanner = new Scanner(System.in);
            mScanner.useDelimiter("\n");
        } catch (UnknownHostException | SocketException e) {
            e.printStackTrace();
        }
    }

    public void start(){
        while (true){
            byte[] buf = new byte[1024];
            try {
                //内容包
                DatagramPacket receivedPacket = new DatagramPacket(buf, buf.length);
                //receive会阻塞
                //从该DatagramSocket中接收数据报
                mSocket.receive(receivedPacket);
                //获取客户端的地址和端口
                InetAddress mAddress = receivedPacket.getAddress();
                int port = receivedPacket.getPort();
                //获取内容
                String clientMsg = new String(receivedPacket.getData(), 0, receivedPacket.getLength());
                System.out.println("客户端address:" + mAddress
                        + " Port:" + port + " 客户端Message:" + clientMsg);

                //返回数据
                String returnedMsg = mScanner.nextLine();
                byte[] returnedMsgBytes = returnedMsg.getBytes();
                //封装返回的数据包
                DatagramPacket sentPacket = new DatagramPacket(returnedMsgBytes, returnedMsgBytes.length, receivedPacket.getSocketAddress());
                mSocket.send(sentPacket);

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        new UdpServer().start();
    }

}

客户端代码：

package com.example.socket_https.udp;

import android.net.InetAddresses;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Scanner;

public class UdpClient {
    private String mServerIp = "192.168.1.4";
    private InetAddress mServerAddress;
    private int mServerPort = 7777;
    private DatagramSocket mSocket;
    private String clientMessage = "";
    private Scanner mScanner;

    public UdpClient(){
        try {
            mSocket = new DatagramSocket();
            mServerAddress = InetAddress.getByName(mServerIp);

            System.out.println("客户端发消息：");
            mScanner = new Scanner(System.in);
            mScanner.useDelimiter("\n");
        } catch (SocketException | UnknownHostException e) {
            e.printStackTrace();
        }
    }

    public void start(){
        while (true){
            String returnedMsg = mScanner.nextLine();
            //将需要发送的String转为bytes
            byte[] returnedMsgBytes = returnedMsg.getBytes();
            try {
                DatagramPacket clientPacket = new DatagramPacket(returnedMsgBytes,
                        returnedMsgBytes.length, mServerAddress, mServerPort);
                //Sent数据
                mSocket.send(clientPacket);

                byte[] buf = new byte[1024];
                DatagramPacket mMsgPacket = new DatagramPacket(buf, buf.length);
                mSocket.receive(mMsgPacket);
                String clientMsg = new String(mMsgPacket.getData(), 0, mMsgPacket.getLength());

                System.out.println("服务端address:" + mSocket.getLocalSocketAddress()
                        + " 服务端 Message:" + clientMsg);

            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        new UdpClient().start();
    }
}