Added ProtectedPlayer.java for storing data on protected players. Created an event for players joining and adding the joined player to a list of protected players.

src/main/java/com/micle/loginprotection/LoginProtection.java

@@ -1,12 +1,17 @@
 package com.micle.loginprotection;
 
+import com.micle.loginprotection.data.ProtectedPlayer;
 import com.micle.loginprotection.setup.Registration;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.fml.common.Mod;
 
+import java.util.ArrayList;
+import java.util.List;
+
 @Mod(LoginProtection.MOD_ID)
 public class LoginProtection {
     public static final String MOD_ID = "loginprotection";
+    public static List<ProtectedPlayer> protected_players = new ArrayList<>();
 
     public LoginProtection() {
         Registration.register();

src/main/java/com/micle/loginprotection/data/ProtectedPlayer.java

@@ -0,0 +1,35 @@
+package com.micle.loginprotection.data;
+
+import java.util.UUID;
+
+public class ProtectedPlayer {
+    private final UUID player_uuid;
+    private int grace_period;
+    private boolean is_loading;
+
+    public ProtectedPlayer(UUID player_uuid) {
+        this.player_uuid = player_uuid;
+        this.grace_period = 200;
+        this.is_loading = true;
+    }
+
+    public UUID getPlayerUUID() {
+        return this.player_uuid;
+    }
+
+    public int getGracePeriod() {
+        return this.grace_period;
+    }
+
+    public void setGracePeriod(int new_grace_period) {
+        this.grace_period = new_grace_period;
+    }
+
+    public boolean isLoading() {
+        return this.is_loading;
+    }
+
+    public void setLoading(boolean new_loading) {
+        this.is_loading = new_loading;
+    }
+}

src/main/java/com/micle/loginprotection/events/OnEntityJoinEventHandler.java

@@ -0,0 +1,18 @@
+package com.micle.loginprotection.events;
+
+import com.micle.loginprotection.LoginProtection;
+import com.micle.loginprotection.data.ProtectedPlayer;
+import net.minecraft.entity.LivingEntity;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraftforge.event.entity.EntityJoinWorldEvent;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+
+public class OnEntityJoinEventHandler {
+    @SubscribeEvent
+    public void EntityJoinWorldEvent(EntityJoinWorldEvent event) {
+        if (!(event.getEntity() instanceof PlayerEntity)) { return; }
+        PlayerEntity player = (PlayerEntity) event.getEntity();
+
+        LoginProtection.protected_players.add(new ProtectedPlayer(player.getUUID()));
+    }
+}

src/main/java/com/micle/loginprotection/setup/Registration.java

@@ -1,10 +1,14 @@
 package com.micle.loginprotection.setup;
 
+import com.micle.loginprotection.events.OnEntityJoinEventHandler;
+import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.eventbus.api.IEventBus;
 import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
 
 public class Registration {
     public static void register() {
         IEventBus mod_event_bus = FMLJavaModLoadingContext.get().getModEventBus();
+
+        MinecraftForge.EVENT_BUS.register(new OnEntityJoinEventHandler());
     }
 }