シンプルバージョン https://github.com/cpslab/TcpMultiSample/tree/simple
cd ./src
javac --enable-preview --source 20 TcpServer.java
java --enable-preview TcpServer
cd ./src
javac --enable-preview --source 20 TcpClient.java
java --enable-preview TcpClient