Added new data class for list of protected players. Created new event for entities getting damaged and made it so that protected players don't take damage.

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

@@ -1,6 +1,7 @@
 package com.micle.loginprotection;
 
 import com.micle.loginprotection.data.ProtectedPlayer;
+import com.micle.loginprotection.data.ProtectedPlayers;
 import com.micle.loginprotection.setup.Registration;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.fml.common.Mod;
@@ -11,7 +12,7 @@ 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 static ProtectedPlayers protected_players = new ProtectedPlayers();
 
     public LoginProtection() {
         Registration.register();

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

@@ -0,0 +1,26 @@
+package com.micle.loginprotection.data;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+public class ProtectedPlayers {
+    private final List<ProtectedPlayer> protected_players = new ArrayList<>();
+
+    public ProtectedPlayers() { }
+
+    public void addPlayer(UUID player_uuid) {
+        protected_players.add(new ProtectedPlayer(player_uuid));
+    }
+
+    public ProtectedPlayer getPlayer(UUID player_uuid) {
+        ProtectedPlayer player = null;
+        for (ProtectedPlayer protected_player : protected_players) {
+            player = protected_player;
+            if (player.getPlayerUUID() == player_uuid) {
+                break;
+            }
+        }
+        return player;
+    }
+}

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

@@ -0,0 +1,18 @@
+package com.micle.loginprotection.events;
+
+import com.micle.loginprotection.LoginProtection;
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.event.entity.living.LivingDamageEvent;
+
+public class OnEntityDamageEventHandler {
+    @SubscribeEvent
+    public void LivingDamageEvent(LivingDamageEvent event) {
+        if (!(event.getEntity() instanceof PlayerEntity)) { return; }
+        PlayerEntity player = (PlayerEntity) event.getEntity();
+
+        if (LoginProtection.protected_players.getPlayer(player.getUUID()) != null) {
+            event.setCanceled(true);
+        }
+    }
+}

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

@@ -13,6 +13,6 @@ public class OnEntityJoinEventHandler {
         if (!(event.getEntity() instanceof PlayerEntity)) { return; }
         PlayerEntity player = (PlayerEntity) event.getEntity();
 
-        LoginProtection.protected_players.add(new ProtectedPlayer(player.getUUID()));
+        LoginProtection.protected_players.addPlayer(player.getUUID());
     }
 }

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

@@ -1,5 +1,6 @@
 package com.micle.loginprotection.setup;
 
+import com.micle.loginprotection.events.OnEntityDamageEventHandler;
 import com.micle.loginprotection.events.OnEntityJoinEventHandler;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.eventbus.api.IEventBus;
@@ -10,5 +11,6 @@ public class Registration {
         IEventBus mod_event_bus = FMLJavaModLoadingContext.get().getModEventBus();
 
         MinecraftForge.EVENT_BUS.register(new OnEntityJoinEventHandler());
+        MinecraftForge.EVENT_BUS.register(new OnEntityDamageEventHandler());
     }
 }