Add: Main, ClientApp, and ServerApp classes for application entry point with primitive input validation

src/main/java/ch/unibas/dmi/dbis/cs108/casono/Main.java

@@ -0,0 +1,42 @@
+package ch.unibas.dmi.dbis.cs108.casono;
+
+import ch.unibas.dmi.dbis.cs108.casono.client.ClientApp;
+import ch.unibas.dmi.dbis.cs108.casono.server.ServerApp;
+
+public final class Main {
+
+    public static void main(String[] args) {
+        if (!isValid(args)) {
+            printUsage();
+            System.exit(1);
+        }
+
+        switch (args[0]) {
+            case "server" -> ServerApp.start(args[1]);
+            case "client" -> ClientApp.start(args[1]);
+            default -> {
+                printUsage();
+                System.exit(1);
+            }
+        }
+    }
+
+    private static boolean isValid(String[] args) {
+        if (args.length != 2) {
+            return false;
+        }
+
+        return switch (args[0]) {
+            case "server", "client" -> true;
+            default -> false;
+        };
+    }
+
+    private static void printUsage() {
+        System.err.println("""
+            Usage:
+              java -jar xyz.jar server <listenPort>
+              java -jar xyz.jar client <serverIp>:<serverPort>
+            """);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/client/ClientApp.java

@@ -0,0 +1,14 @@
+package ch.unibas.dmi.dbis.cs108.casono.client;
+
+public class ClientApp {
+    public static void start(String arg) {
+        String[] parts = arg.split(":", 2);
+        if (parts.length != 2) {
+            throw new IllegalArgumentException("Address must be in format <ip>:<port>.");
+        }
+        String host = parts[0];
+        int port = Integer.parseInt(parts[1]);
+
+        System.out.println("You've selected the client. It will connect port " + port + " at host " + host);
+    }
+}

src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/ServerApp.java

@@ -0,0 +1,8 @@
+package ch.unibas.dmi.dbis.cs108.casono.server;
+
+public class ServerApp {
+    public static void start(String arg) {
+        int port = Integer.parseInt(arg);
+        System.out.println("You've selected the server. It will accept connections at port" + port);
+    }
+}